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Real Numbers · Real Numbers

Scientific Notation

Before you start, make sure you know: Powers with integer exponents (Algebra 2)
Before you start, make sure you know: Properties of powers (Algebra 2)

Multiply 5,000,000 by 50,000,000 on a calculator and it does not show the 15-digit answer. It shows something like 2.5E14. What does that mean, and how do scientists write a number like the mass of an electron, which has 30 zeros after the decimal point? Scientific notation is the shorthand that makes numbers at every scale easy to read, compare and compute with.

What is scientific notation?

Two details: $a = 1$ is allowed (so $1 \times 10^6$ is fine), but $a = 10$ is not. Negative numbers keep their sign: the condition is on $|a|$, so $-4.52 \times 10^{-7}$ is correct.

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Write the following numbers in standard form, adjusting the mantissa so that it is between $1$ and $10$: a) $0,000000456$ b) $34500000000$ c) $0,0023 \cdot 10^5$ d)…

Write the following numbers in standard form, adjusting the mantissa so that it is between $1$ and $10$:

  1. a) $0,000000456$
  2. b) $34500000000$
  3. c) $0,0023 \cdot 10^5$
  4. d) $456 \cdot 10^{-4}$
Solve
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Justify whether the following expressions are correctly written in standard form. If not, correct them so that the mantissa $N$ satisfies $1 \le |N| < 10$: a)…

Justify whether the following expressions are correctly written in standard form. If not, correct them so that the mantissa $N$ satisfies $1 \le |N| < 10$:

  1. a) $12,4 \cdot 10^3$
  2. b) $0,85 \cdot 10^{-2}$
  3. c) $1 \cdot 10^6$
  4. d) $-45,2 \cdot 10^{-8}$
Solve

Converting between decimal form and scientific notation

The exponent counts how many places the decimal point moves. A number greater than 10 gets a positive exponent. A number between 0 and 1 gets a negative exponent. When units change, convert them too: the exponent from the units and the exponent from the decimal point add up.

Two conversions to scientific notation: 0.07 millimeters to meters, and 320 billion dollars 0.07 mm = 7 · 10⁻⁵ m 2 places (decimal point) + 3 places (mm → m) = 5 places to the left 320 billion dollars = 3.2 · 10¹¹ dollars 320 · 10⁹ = 3.2 · 10² · 10⁹ = 3.2 · 10¹¹

Number words in the US: a million is $10^6$, a billion is $10^9$, and a trillion is $10^{12}$.

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The diameter of a human red blood cell is approximately $0,0075$ mm. Express this quantity in meters using standard form.

The diameter of a human red blood cell is approximately $0,0075$ mm. Express this quantity in meters using standard form.

Solve
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The estimated fortune of one of the richest people in the technology sector amounts to $185000$ million dollars. Write this figure in standard form.

The estimated fortune of one of the richest people in the technology sector amounts to $185000$ million dollars. Write this figure in standard form.

Solve

Significant figures and order of magnitude

Measurements are never perfectly exact. Significant figures tell you which digits of a measurement mean something.

The number 0.004050 with its leading zeros in gray and its four significant digits highlighted, written as 4.050 times 10 to the minus 3 0.004050 = 4.050 · 10⁻³ leading zeros only locate the decimal point every digit in the coefficient counts: 4 significant figures

The order of magnitude of a number is the exponent $n$ in its scientific notation. For example, $7.30 \times 10^{-3}$ s has order of magnitude $-3$ and 3 significant figures.

To round to $s$ significant figures, write the number in scientific notation, keep $s$ digits of the coefficient, and look at the next digit. If it is 5 or more, round up.

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State the order of magnitude and the number of significant figures of the following experimental measurements: a) $4,05 \cdot 10^8$ m b) $1,200 \cdot 10^{-5}$ kg c)…

State the order of magnitude and the number of significant figures of the following experimental measurements:

  1. a) $4,05 \cdot 10^8$ m
  2. b) $1,200 \cdot 10^{-5}$ kg
  3. c) $9 \cdot 10^{12}$ s
Solve
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Round the following numbers so that they have exactly three significant figures and then express them in standard form: a) $4567892$ b) $0,00034091$ c) $98,99$

Round the following numbers so that they have exactly three significant figures and then express them in standard form:

  1. a) $4567892$
  2. b) $0,00034091$
  3. c) $98,99$
Solve

Comparing numbers

Scientific notation makes comparing easy, because the exponent tells you the size class.

A logarithmic number line with ticks at 10 to the 3rd through 10 to the 6th, showing 7 times 10 to the 3rd and 2 times 10 to the 4th 10³10⁴10⁵10⁶ 7·10³ 2·10⁴ each tick is 10 times the previous one

If the numbers are not in scientific notation yet, rewrite them first. For negative numbers the order flips: the number with the larger absolute value is smaller.

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Order the following numbers from smallest to largest, first converting them to normalized standard form and comparing their orders of magnitude:…

Order the following numbers from smallest to largest, first converting them to normalized standard form and comparing their orders of magnitude:

$A = 0,0045 \cdot 10^{-3}$

$B = 450 \cdot 10^{-8}$

$C = 0,45 \cdot 10^{-5}$

$D = 45000 \cdot 10^{-11}$

Solve

Multiplying and dividing

Multiplying 6 times 10 to the 8 by 4 times 10 to the minus 3: multiply the coefficients, add the exponents, then adjust 6 · 10⁸ · 4 · 10⁻³ = 24 · 10⁵ = 2.4 · 10⁶ coefficients: multiply powers of 10: add the exponents
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Work out the following multiplications and divisions mentally (without using a calculator), applying the properties of powers, and express the result in standard form:…

Work out the following multiplications and divisions mentally (without using a calculator), applying the properties of powers, and express the result in standard form:

  1. a) $(3 \cdot 10^4) \cdot (2 \cdot 10^5)$
  2. b) $\frac{8 \cdot 10^{-3}}{4 \cdot 10^{-7}}$
  3. c) $(1,5 \cdot 10^6) \cdot (4 \cdot 10^{-2})$
Solve
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The mass of the Earth is approximately $5,97 \cdot 10^{24}$ kg and that of the planet Jupiter is $1,90 \cdot 10^{27}$ kg. How many times more massive is Jupiter than the…

The mass of the Earth is approximately $5,97 \cdot 10^{24}$ kg and that of the planet Jupiter is $1,90 \cdot 10^{27}$ kg. How many times more massive is Jupiter than the Earth? Express the result in standard form and also in standard decimal format.

Solve

Adding and subtracting

You can only add or subtract like quantities. In scientific notation that means the same power of 10. Then factor it out, just as $3x + 5x = (3 + 5)x$:

$$a \times 10^n \pm b \times 10^n = (a \pm b) \times 10^n.$$ Adding 3.4 times 10 to the 6 and 5.1 times 10 to the 7 by first rewriting both with the same exponent 3.4 · 10⁶ + 5.1 · 10⁷ different exponents: you can't add the coefficients yet 0.34 · 10⁷ + 5.1 · 10⁷ = (0.34 + 5.1) · 10⁷ = 5.44 · 10⁷
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Work out the following additions and subtractions of numbers in standard form that have the same exponent. Take out the common factor and give the final result: a)…

Work out the following additions and subtractions of numbers in standard form that have the same exponent. Take out the common factor and give the final result:

  1. a) $3,2 \cdot 10^5 + 4,5 \cdot 10^5$
  2. b) $8,7 \cdot 10^{-4} - 3,2 \cdot 10^{-4}$
  3. c) $5,15 \cdot 10^{12} + 2,03 \cdot 10^{12}$
Solve
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Work out the following additions and subtractions by first adjusting the exponents to be able to take out a common factor. Express the final result in standard form: a)…

Work out the following additions and subtractions by first adjusting the exponents to be able to take out a common factor. Express the final result in standard form:

  1. a) $4,5 \cdot 10^7 + 3,8 \cdot 10^8$
  2. b) $9,2 \cdot 10^{-5} - 6,1 \cdot 10^{-6}$
Solve
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Work out the following combined operation and express the final result in standard form, rounding to three significant figures:…

Work out the following combined operation and express the final result in standard form, rounding to three significant figures:

$\frac{(2,5 \cdot 10^6) \cdot (4,2 \cdot 10^{-3})}{3,1 \cdot 10^{-4} + 1,9 \cdot 10^{-5}}$

Solve

Powers and roots

When a problem says exactly, keep every digit of the result. For example, $5^8 = 390{,}625 = 3.90625 \times 10^5$ exactly. Rounding to 3 significant figures would give $3.91 \times 10^5$, which is only an approximation.

Computer storage uses powers of $1024 = 2^{10}$, so exact computations are powers of 2.

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A server hard drive has a storage capacity of $2$ TB (Terabytes). Given that $1\text{ TB} = 1024\text{ GB}$, $1\text{ GB} = 1024\text{ MB}$,…

A server hard drive has a storage capacity of $2$ TB (Terabytes). Given that $1\text{ TB} = 1024\text{ GB}$, $1\text{ GB} = 1024\text{ MB}$, $1\text{ MB} = 1024\text{ KB}$ and $1\text{ KB} = 1024\text{ B}$ (Bytes). Calculate exactly how many bytes the hard drive can store and express the result in standard form.

Solve
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Given the physical quantities $A = 3,2 \cdot 10^5$ and $B = 5,1 \cdot 10^{-4}$, calculate the value of the algebraic expression $\frac{A^3}{\sqrt{B}}$. Express the final…

Given the physical quantities $A = 3,2 \cdot 10^5$ and $B = 5,1 \cdot 10^{-4}$, calculate the value of the algebraic expression $\frac{A^3}{\sqrt{B}}$. Express the final result in standard form with three significant figures and clearly state its order of magnitude.

Solve

Units and rates

Most science problems need a unit conversion. Write each conversion factor in scientific notation, multiply, and keep track of the exponent. Dividing two quantities also gives a rate: dividing total mass by number of molecules gives the mass of one molecule.

A cube with edge 1 kilometer, which is 10 to the 5 centimeters, so its volume is 10 to the 15 cubic centimeters 1 km = 10⁵ cm 1 km³ = (10⁵ cm)³ = 10¹⁵ cm³
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The speed of light in a vacuum is approximately $3 \cdot 10^5$ km/s. A "light year" is the distance that light travels in a vacuum during one Earth year ($365,25$ days).…

The speed of light in a vacuum is approximately $3 \cdot 10^5$ km/s. A "light year" is the distance that light travels in a vacuum during one Earth year ($365,25$ days). Calculate how many kilometers a light year is equivalent to and express the result in standard form with four significant figures.

Solve
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Given that $18$ grams of water contain $6,022 \cdot 10^{23}$ molecules (Avogadro's number), calculate the mass in grams of a single water molecule. Give the result in…

Given that $18$ grams of water contain $6,022 \cdot 10^{23}$ molecules (Avogadro's number), calculate the mass in grams of a single water molecule. Give the result in standard form with four significant figures.

Solve
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The total volume of water in all the Earth's oceans is estimated at $1,332 \cdot 10^9\text{ km}^3$. If we assume that a standard drop of water has an average volume of…

The total volume of water in all the Earth's oceans is estimated at $1,332 \cdot 10^9\text{ km}^3$. If we assume that a standard drop of water has an average volume of $0,05$ ml, determine the total number of drops of water in the oceans. Express the result in standard form. (Remember that $1\text{ ml} = 1\text{ cm}^3$).

Solve

Errors and intervals

When a measurement is only known to lie in an interval $[L, U]$, apply the formula to both endpoints. For positive quantities and an increasing formula (area, volume), the interval for the result runs from the value at $L$ to the value at $U$. If you use the midpoint as your estimate, the error bound is half the width of the interval.

A number line showing an interval from 2.025 to 2.116, its midpoint 2.0705, and the error bound as half the width (all × 10⁻³ m²) 2.025 2.0705 2.116 min estimate max error bound = 0.0455 · 10⁻³ m² = 4.55 · 10⁻⁵ m²
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When measuring the distance between two cities using a GPS system, a real value of $456321$ m is obtained. A tourist map approximates this distance giving a value of…

When measuring the distance between two cities using a GPS system, a real value of $456321$ m is obtained. A tourist map approximates this distance giving a value of $4,56 \cdot 10^5$ m. Calculate the absolute error and the relative error made when using the map's approximation. Express both errors in standard form.

Solve
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The edge of a perfect cube has been measured with a precision instrument and its length is known to be in the interval $[1,25 \cdot 10^{-2}, 1,26 \cdot 10^{-2}]$ m.…

The edge of a perfect cube has been measured with a precision instrument and its length is known to be in the interval $[1,25 \cdot 10^{-2}, 1,26 \cdot 10^{-2}]$ m. Determine the interval in which the volume of the cube lies, expressed in $\text{mm}^3$, giving the endpoints in standard form. Calculate the absolute error bound if we take the midpoint of this interval as the estimated volume.

Solve

Huge numbers, logarithms and e

Some numbers are too large for a calculator to even display, like $3^{100}$. Logarithms handle them, because they turn powers into products.

The logarithm 47.712 split into its integer part, which gives the exponent, and its decimal part, which gives the coefficient log N = 47.712 integer part 47 → exponent n = 47 decimal part 0.712 → coefficient 10⁰·⁷¹² ≈ 5.15 N ≈ 5.15 · 10⁴⁷
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A maximum security encryption algorithm uses $256$-bit keys, which means that the total number of possible keys is $2^{256}$. Using the properties of common logarithms…

A maximum security encryption algorithm uses $256$-bit keys, which means that the total number of possible keys is $2^{256}$. Using the properties of common logarithms and given that $\log_{10} 2 \approx 0,30103$, express the total number of combinations in standard form $N \cdot 10^n$, where $1 \le N < 10$.

Solve
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The energy released by an earthquake is empirically related to its magnitude $M$ on the Richter scale by the formula $\log_{10} E = 11,8 + 1,5M$, where $E$ is measured…

The energy released by an earthquake is empirically related to its magnitude $M$ on the Richter scale by the formula $\log_{10} E = 11,8 + 1,5M$, where $E$ is measured in ergs. Calculate the energy released by an earthquake of magnitude $7,5$ and by another of magnitude $8,5$. How many times greater is the energy of the second compared to the first? Express the energy results in standard form.

Solve
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A sample of radioactive material used in fossil dating initially contains $N_0 = 4,5 \cdot 10^{20}$ nuclei. The number of nuclei decays exponentially according to the…

A sample of radioactive material used in fossil dating initially contains $N_0 = 4,5 \cdot 10^{20}$ nuclei. The number of nuclei decays exponentially according to the law $N(t) = N_0 \cdot e^{-\lambda t}$, where $\lambda = 3,2 \cdot 10^{-4}\text{ years}^{-1}$. Calculate the number of nuclei that will remain undecayed after $5000$ years. Express the final result in standard form with two significant figures.

Solve

Science formulas and growth

Real science formulas combine everything above. Convert units first, then handle coefficients and powers of 10 separately, and round once at the end.

A proton and an electron separated by a distance r, with the formula for the electric force between them + − r = 5.3 · 10⁻¹¹ m F = k q₁ q₂ / r² k = 8.99 · 10⁹ N·m²/C², q = 1.6 · 10⁻¹⁹ C

When two quantities grow at different rates (for example, total income and population), grow each one separately, then divide.

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Newton's law of universal gravitation states that the force of attraction between two masses is $F = G \frac{m_1 m_2}{d^2}$. Given that the constant…

Newton's law of universal gravitation states that the force of attraction between two masses is $F = G \frac{m_1 m_2}{d^2}$. Given that the constant $G = 6,67 \cdot 10^{-11}\text{ N}\cdot\text{m}^2/\text{kg}^2$, the mass of the Earth is $m_1 = 5,97 \cdot 10^{24}$ kg, the mass of the Moon is $m_2 = 7,35 \cdot 10^{22}$ kg and the mean distance between their centers is $d = 3,84 \cdot 10^5$ km. Calculate the force of attraction $F$ in Newtons, using standard form in all intermediate calculations.

Solve
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The global Gross Domestic Product (GDP) in a given year was approximately $8,5 \cdot 10^{13}$ dollars. If the world population at that time was $7,8 \cdot 10^9$…

The global Gross Domestic Product (GDP) in a given year was approximately $8,5 \cdot 10^{13}$ dollars. If the world population at that time was $7,8 \cdot 10^9$ inhabitants, calculate the average GDP per capita. If the population is projected to grow by $1,2\%$ annually and the GDP to grow by $2,5\%$ annually, estimate the GDP per capita after $10$ years. Express all results in standard form.

Solve

Back to the start: 2.5E14 on a calculator means $2.5 \times 10^{14}$. The mass of an electron, $9.11 \times 10^{-31}$ kg, would need 30 zeros after the decimal point. The distance to Proxima Centauri, $4.02 \times 10^{16}$ m (about 25 trillion miles), would need 17 digits before the decimal point. Scientific notation turns both into short numbers whose size you can read from the exponent.

Summary

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