Rational Numbers
Your phone shows 75% battery, the pizza place sells three quarters of a pizza per person, and your GPS says you've gone two thirds of the way. All of these are fractions: numbers we use to talk about parts. You already know them from Secondary Year 1 and Year 2; here you'll review them so you can handle them with ease, since they're the foundation of almost everything that comes next.
What Is a Rational Number?
A fraction $\frac{a}{b}$ has two parts: the denominator $b$ tells you how many equal parts we split the whole into, and the numerator $a$ tells you how many we take.
The same fraction can be read in three ways, and it's good to keep all of them in mind:
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Part of a whole: $\frac{3}{4}$ of a pizza is 3 slices of a pizza cut into 4.
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Quotient: $\frac{3}{4} = 3 \div 4 = 0.75$. That's why your battery at 75% is at $\frac{3}{4}$.
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Operator: $\frac{3}{4}$ of 200 pesos is $200 \times \frac{3}{4} = 150$ pesos.
Integers are rational too: $5 = \frac{5}{1}$ and $-2 = \frac{-4}{2}$. And a fraction can be negative: $-\frac{3}{4} = \frac{-3}{4} = \frac{3}{-4}$ (you can put the sign wherever you like, but it's usually placed in front).
Play with the numerator and the denominator. Notice what happens when the numerator is greater than the denominator: the fraction is worth more than one whole (an improper fraction).
In a strategy video game, the map is divided into different zones according to the terrain. The total map occupies 1 200 square pixels. The forest occupies $\frac{1}{3}$…
In a strategy video game, the map is divided into different zones according to the terrain.
The total map occupies 1 200 square pixels.
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The forest occupies $\frac{1}{3}$ of the map.
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The water occupies $\frac{1}{4}$ of the map.
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The remainder is desert.
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How many square pixels does the forest occupy?
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How many square pixels does the water occupy?
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Work out what irreducible fraction of the map represents the desert.
Equivalent Fractions
Half a pizza, two quarters, or four eighths: it's the same amount of pizza, even though it's cut differently. These are equivalent fractions.
If you multiply or divide the numerator and the denominator by the same number, you get an equivalent fraction. Dividing is called simplifying. When you can't simplify any further, you have the fraction in lowest terms: the cleanest way to write that number.
Look at the following graphical representation of a fraction. Your task is to: 1. Write down the irreducible fraction that represents the section coloured orange…
Look at the following graphical representation of a fraction. Your task is to:
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Write down the irreducible fraction that represents the section coloured orange compared to the total circle.
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State whether the fraction $\frac{9}{24}$ is equivalent to the one represented in the image. Justify your answer by simplifying both fractions.
Comparing and Ordering Fractions
Who ate more: the person who eats $\frac{3}{4}$ of a chocolate bar or the one who eats $\frac{5}{7}$? At a glance it's not clear. Look at the bars:
By a small margin, $\frac{3}{4}$ is greater. But you won't always be able to draw a picture, so you need a method.
Three friends are competing in a 100-meter obstacle race. At a given moment, their positions are as follows: Ana has covered $\frac{2}{5}$ of the total distance. Beto…
Three friends are competing in a 100-meter obstacle race. At a given moment, their positions are as follows:
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Ana has covered $\frac{2}{5}$ of the total distance.
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Beto has covered $\frac{3}{4}$ of the total distance.
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Carla has covered $\frac{7}{10}$ of the total distance.
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Calculate how many meters each person has covered exactly.
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Order the fractions from smallest to largest using the symbol $<$.
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Mark the approximate positions of Ana (A), Beto (B), and Carla (C) on the number line shown below.
Plotting Fractions on the Number Line
Every rational number has its exact place on the number line. To place $\frac{7}{4}$:
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If it's improper, pull out the whole numbers: $\frac{7}{4} = 1 + \frac{3}{4}$. It lies between 1 and 2.
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Divide the segment from 1 to 2 into 4 equal parts (the denominator).
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Count 3 of those parts (the numerator of the remainder).
And what if you need to divide a segment into exactly 7 parts, without a ruler with markings? You use the Thales theorem (intercept theorem): you draw an auxiliary ray from 0, mark 7 equal steps with a compass, connect the last mark to 1, and draw parallel lines. You'll see it in the geometry chapter.
Try dragging the point: you'll see which fraction and which decimal correspond to each position.
Represent the rational numbers $\frac{7}{4}$ and $-\frac{2}{3}$ on the number line. To do so, use Thales' Theorem or the division of segments to place the points…
Represent the rational numbers $\frac{7}{4}$ and $-\frac{2}{3}$ on the number line.
To do so, use Thales' Theorem or the division of segments to place the points exactly, not approximately.
Draw in your notebook a line like the following one, with the integers marked (it is best for the unit to be large, for example 6 cm), and carry out your construction on it:
You can do it on paper and send a photo with your answer.
Adding and Subtracting Fractions
Adding fractions is like combining pesos and dollars: before adding, you have to convert everything to the same currency. Here the "currency" is the denominator.
Perform the following operations with fractions. Remember that to add or subtract, you must first find the lowest common multiple (LCM) of the denominators. Express the…
Perform the following operations with fractions. Remember that to add or subtract, you must first find the lowest common multiple (LCM) of the denominators. Express the result as an irreducible fraction.
- a) $\frac{2}{3} + \frac{1}{6}$
- b) $\frac{4}{5} - \frac{1}{2}$
- c) $\frac{3}{4} + \frac{5}{12} - \frac{1}{3}$
The storage on your cell phone is divided as follows: Photos occupy $\frac{2}{5}$ of the space. Applications occupy $\frac{1}{3}$ of the space. 1. What fraction of the…
The storage on your cell phone is divided as follows:
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Photos occupy $\frac{2}{5}$ of the space.
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Applications occupy $\frac{1}{3}$ of the space.
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What fraction of the total do photos and applications occupy together?
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If the rest of the space is free, what fraction represents the free space?
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If the total capacity of the phone is 60 GB, how many GB are left free?
Multiplying and Dividing Fractions
Multiplying is easier than adding: numerator times numerator and denominator times denominator. The picture explains why: $\frac{2}{3}$ of $\frac{3}{4}$ is the region where the two strips overlap.
Calculate the following products and divisions of fractions. Remember to simplify the final result if possible. a) $\frac{3}{4} \times \frac{8}{9}$ b)…
Calculate the following products and divisions of fractions. Remember to simplify the final result if possible.
- a) $\frac{3}{4} \times \frac{8}{9}$
- b) $\frac{2}{5} : \frac{4}{15}$
- c) $\frac{5}{6} \times (-2)$
Note: Remember the rule of signs and that an integer has a denominator of 1.
Three friends buy a birthday present costing 1,200 pesos. Ana contributes $\frac{1}{3}$ of the total price. Beto contributes $\frac{2}{5}$ of the total price. Carla pays…
Three friends buy a birthday present costing 1,200 pesos.
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Ana contributes $\frac{1}{3}$ of the total price.
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Beto contributes $\frac{2}{5}$ of the total price.
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Carla pays the rest.
- a) What fraction of the total does Carla pay?
- b) How much money in pesos does each person contribute?
Combined Operations
When operations are mixed, there is a mandatory order. If you don't follow it, each person would get a different result from the same calculation.
Within the same level, work from left to right.
Calculate the value of the following combined operation, following the order of operations (brackets, powers, multiplication/division, addition/subtraction). You must…
Calculate the value of the following combined operation, following the order of operations (brackets, powers, multiplication/division, addition/subtraction). You must simplify the final result to obtain the irreducible fraction.
$$ \left( \frac{3}{2} - \frac{1}{4} \right)^2 : \frac{5}{8} - \left( 1 - \frac{3}{5} \times \frac{10}{3} \right) $$Your cell phone has an unknown total storage capacity. The operating system occupies $\frac{1}{6}$ of the total memory. Of what remains free, your applications and games…
Your cell phone has an unknown total storage capacity. The operating system occupies $\frac{1}{6}$ of the total memory. Of what remains free, your applications and games occupy $\frac{3}{5}$. If in the end you have 32 GB free for your photos and videos:
- a) What fraction of the total represents the free memory for photos?
- b) What is the total storage capacity of the phone in GB?
Use the following diagram to help you visualize the problem: