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Secondary 2 · Mathematics
Numbers · Integers

Representing Integers on the Number Line

Before you start, make sure you know: Representation on the number line (Secondary Year 1)
Before you start, make sure you know: Operations with integers (Secondary Year 1)

On the Mexico City Metro, a young man gets on at the Zócalo station and travels three stations west and then two stations east. Where does he end up? How many stations is he from where he started? A number line answers both questions at a glance. Here you will learn to use it to order numbers, measure distances, and describe whole stretches.

Representing integers on the number line

On the number line, $0$ is the origin. Positive numbers are to the right and negative numbers are to the left. The farther to the right a number is, the greater it is.

Number line showing that the opposite numbers −4 and +4 are at the same distance of 4 units from the origin. −4 0 +4 same distance from 0: are opposites 4 4

To order numbers, place them on the line and read them from left to right: each one is less than the one to its right. For example, $-6 < -3 < -1 < 2 < 4$.

Movements are drawn as arrows: adding a positive number means moving right, and adding a negative number means moving left.

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Look at the following number line and identify the values represented by the letters $A$, $B$ and $C$.

Look at the following number line and identify the values represented by the letters $A$, $B$ and $C$.

0 1 A B C
Solve
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Draw a number line in your notebook and represent the following integers on it: $$-4, \quad +3, \quad 0, \quad -1, \quad +5$$ You can do it on paper and send a photo…

Draw a number line in your notebook and represent the following integers on it:

$$-4, \quad +3, \quad 0, \quad -1, \quad +5$$

You can do it on paper and send a photo with your answer.

Solve
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A thermometer shows a temperature of $4^\circ\text{C}$ at ten in the morning. If at eight in the evening the temperature has dropped by $6^\circ\text{C}$, represent both…

A thermometer shows a temperature of $4^\circ\text{C}$ at ten in the morning. If at eight in the evening the temperature has dropped by $6^\circ\text{C}$, represent both temperatures on a line and indicate the final temperature.

Solve
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Represent the number $-3$ and its opposite on the number line. How far is each one from the origin? You can use this number line, in which the origin and the units are…

Represent the number $-3$ and its opposite on the number line. How far is each one from the origin?

You can use this number line, in which the origin and the units are marked (each mark is one unit), or draw your own:

Number line with unit marks from -5 to 5, with the origin 0 and the 1 labeled 0 1

You can do it on paper and send a photo with your answer.

Solve
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A scuba diver is at a depth of $8$ meters below sea level. If they decide to go up $3$ meters to look at some fish, what depth are they at now? Represent the movement…

A scuba diver is at a depth of $8$ meters below sea level. If they decide to go up $3$ meters to look at some fish, what depth are they at now? Represent the movement using arrows on a horizontal number line.

Sea level ← Depth (-) Surface (+) −8 0 Start
Solve
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Place the following numbers on the number line and use it to order them from least to greatest using the symbol $<$: $$-6, \quad +2, \quad -3, \quad +4, \quad -1$$

Place the following numbers on the number line and use it to order them from least to greatest using the symbol $<$:

$$-6, \quad +2, \quad -3, \quad +4, \quad -1$$
Solve
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On the following number line, four points represented by letters have been marked. Identify which integer corresponds to each of the letters $A$, $B$, $C$, and $D$.

On the following number line, four points represented by letters have been marked. Identify which integer corresponds to each of the letters $A$, $B$, $C$, and $D$.

0 A B C D
Solve
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A food delivery driver begins his shift at "Point Zero" on a main avenue. He makes the following trips: 1. Travels $4$ kilometers to the east ($+4$). 2. From there,…

A food delivery driver begins his shift at "Point Zero" on a main avenue. He makes the following trips:

  1. Travels $4$ kilometers to the east ($+4$).

  2. From there, travels $7$ kilometers to the west.

  3. Finally, travels another $2$ kilometers to the west to deliver his last order.

Draw a number line in your notebook, represent each movement using arrows, and determine which kilometer mark he is at when finished.

−6 −5 −4 −3 −2 −1 0 1 2 3 4 5 6 Start +4 km −7 km −2 km
Solve
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Draw a number line and place the following elements on it. Then, order them from least to greatest using the symbol $<$: The number $-4$. The opposite of $3$. The…

Draw a number line and place the following elements on it. Then, order them from least to greatest using the symbol $<$:

  • The number $-4$.

  • The opposite of $3$.

  • The absolute value of $-5$.

  • The number $0$.

  • The opposite of the opposite of $-2$.

You can do it on paper and send a photo with your answer.

Solve

Distance between two points

Number line illustrating the distance between two integers as the length of the segment between them. −6 0 +3 distance = 6 + 3 = 9 6 3

A midpoint is at the same distance from both endpoints: you get it by adding the endpoints and dividing by $2$. Between $-7$ and $3$ it is $\frac{-7+3}{2} = -2$. Check: $-2$ is $5$ away from both.

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In a ski resort in Sierra Nevada, the thermometer recorded the following temperatures throughout the morning: At 8:00: $-6$ $^\circ$C At 10:00: $-2$ $^\circ$C At 12:00:…

In a ski resort in Sierra Nevada, the thermometer recorded the following temperatures throughout the morning:

  • At 8:00: $-6$ $^\circ$C

  • At 10:00: $-2$ $^\circ$C

  • At 12:00: $+3$ $^\circ$C

  1. a) Represent the three temperatures on a vertical number line (like a thermometer).
  2. b) What was the temperature change (distance on the line) between 8:00 and 12:00?
Solve
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Find the integer that is exactly the same distance from $-7$ and from $+3$ on the number line. In the figure those two numbers are marked. Represent it graphically on…

Find the integer that is exactly the same distance from $-7$ and from $+3$ on the number line. In the figure those two numbers are marked. Represent it graphically on the line to check your result and explain how you calculated it.

Number line with the integers from −7 to 3, with the points −7 and 3 marked in blue−6−5−4−3−2−1012−73
Solve
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A submarine and a rescue helicopter are positioned on the same vertical line. If we transpose their positions to a horizontal number line where $0$ is sea level: The…

A submarine and a rescue helicopter are positioned on the same vertical line. If we transpose their positions to a horizontal number line where $0$ is sea level:

  • The submarine is located at point $S$.

  • The helicopter is located at point $H$.

  • It is known that $|S| = |H| - 200$.

  • The distance between the submarine and the helicopter is $500$ meters.

Draw the number line and find the coordinates of $S$ and $H$, knowing that the helicopter flies above sea level and the submarine is submerged.

|H| |S| |S| 200 m 0 Sea level S |S| H 500 m Submarine (-) Helicopter (+)
Solve
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On the number line of integers, point $A$ represents the number $-4$. Point $B$ is a number such that its distance from the origin is three times the distance of $A$…

On the number line of integers, point $A$ represents the number $-4$. Point $B$ is a number such that its distance from the origin is three times the distance of $A$ from the origin. If point $C$ is the midpoint of the line segment formed by the opposite points of $A$ and $B$, which numbers could $C$ represent? Note that there are two possible solutions for $B$. Represent them graphically.

Solve

Inequalities and stretches of the number line

A condition such as $-2 < x \le 3$ describes all the integers in a stretch of the line at once.

Number line with the stretch between −2 (open circle, excluded) and +3 (filled circle, included). −3 −2 −1 0 1 2 +3 4 −2 not included +3 included length 5
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Write in your notebook all the integers $x$ that satisfy the condition $-2 < x \leq 3$ and represent them on the number line. Pay close attention to the open and closed…

Write in your notebook all the integers $x$ that satisfy the condition $-2 < x \leq 3$ and represent them on the number line. Pay close attention to the open and closed endpoints.

You can copy this number line into your notebook:

Empty number line with the integer marks from −4 to 4−4−3−2−101234
Solve
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Write down all the integers $x$ that satisfy the following two conditions simultaneously and represent them on a number line: $-5 < x \leq 2$ The absolute value of $x$…

Write down all the integers $x$ that satisfy the following two conditions simultaneously and represent them on a number line:

  • $-5 < x \leq 2$

  • The absolute value of $x$ is greater than $1$, that is, $|x| > 1$.

Solve
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Identify all the integers $n$ that satisfy the following three conditions simultaneously and plot them on a number line: 1. The absolute value of $n$ is less than or…

Identify all the integers $n$ that satisfy the following three conditions simultaneously and plot them on a number line:

  1. The absolute value of $n$ is less than or equal to $7$: $|n| \leq 7$.

  2. $n$ is strictly greater than its opposite: $n > -n$.

  3. The distance between $n$ and the number $-2$ is greater than $5$ units.

Solve
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Draw a number line and represent the following sets of numbers so that the difference between them can be seen (for example, by using a different color for each set):…

Draw a number line and represent the following sets of numbers so that the difference between them can be seen (for example, by using a different color for each set):

  • Set $X$: integers $x$ such that $|x| < 4$.

  • Set $Y$: integers $y$ such that their opposite $-y$ is between $-2$ and $5$ (both excluded).

State, with reasoning, which integers belong to both sets at the same time.

You can do it on paper and send a photo with your answer.

Solve

Absolute value on the number line

The equation $|x| = 4$ has two solutions: the two points that are at distance $4$ from $0$.

Number line with the two solution points, −4 and +4, located at distance 4 from the origin. −4 0 +4 same distance from 0 d d

Similarly, $|x - 3| = 5$ asks for the points at distance $5$ from the number $3$: one to the right and one to the left.

Inequalities with absolute value

Since $|x|$ is the distance from $x$ to $0$, an inequality with absolute value describes a stretch of the number line:

  • $|x| < k$ means "less than $k$ units from $0$": the numbers between $-k$ and $k$, that is, $-k < x < k$.

  • $|x| > k$ means "more than $k$ units from $0$": the ones that lie outside that stretch, that is, $x < -k$ or $x > k$.

  • With $\le$ or $\ge$, the endpoints $-k$ and $k$ are included (filled circle).

Two number lines: on top, the stretch between −3 and 3 for |x| less than 3; below, the stretches outside −3 and 3 for |x| greater than 3. −3 0 3 |x| < 3: inside the stretch −3 0 3 |x| > 3: outside the stretch
Practice★☆☆Not started
Represent on the number line all the integers whose absolute value is equal to $4$. How many numbers have you marked? You can do it on paper and send a photo with your…

Represent on the number line all the integers whose absolute value is equal to $4$. How many numbers have you marked?

You can do it on paper and send a photo with your answer.

Solve
Practice★★☆Not started
Represent the number $-3$ and all the integers whose absolute value is less than it on the number line. Is it possible to complete this task? Justify your answer based…

Represent the number $-3$ and all the integers whose absolute value is less than it on the number line. Is it possible to complete this task? Justify your answer based on the definition of absolute value and its graphical representation.

You can do it on paper and send a photo with your answer.

Solve
Practice★★☆Not started
Given the integers $x$ whose distance from the origin ($0$) is $6$ units, and using the number line in the figure (or drawing an identical one in your notebook): a)…

Given the integers $x$ whose distance from the origin ($0$) is $6$ units, and using the number line in the figure (or drawing an identical one in your notebook):

  1. a) Represent those numbers on the number line.
  1. b) Also represent their opposites.
  1. c) What do you notice about the position of the original numbers and their opposites on the line?
Number line graduated from −8 to 8 with the origin marked−8−7−6−5−4−3−2−1012345678
Solve
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Given the following expressions, plot on the number line the values of $x$ that make them true: a) $|x - 3| = 5$ b) $|x + 2| = 4$ Which integer is a solution to both…

Given the following expressions, plot on the number line the values of $x$ that make them true:

  1. a) $|x - 3| = 5$
  2. b) $|x + 2| = 4$

Which integer is a solution to both expressions at the same time? Mark it in a different color on your number line.

−8 −7 −6 −5 −4 −3 −2 −1 0 1 2 3 4 5 6 7 8 9 10 a) |x - 3| = 5 center = 3 distance = 5 distance = 5 b) |x + 2| = 4 center = −2 distance = 4 distance = 4
Solve
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Consider a negative integer $a$ and a positive integer $b$. On the number line, the distance between $a$ and $b$ is $15$ units. If the absolute value of $a$ is double…

Consider a negative integer $a$ and a positive integer $b$. On the number line, the distance between $a$ and $b$ is $15$ units. If the absolute value of $a$ is double the absolute value of $b$, that is, $|a| = 2 \times |b|$, find the values of $a$ and $b$ and represent them. What is the opposite of the sum $a + b$?

Solve
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Three points $P$, $Q$, and $R$ are located on the number line. It is known that: Point $Q$ is the opposite of $-6$. Point $P$ is at a distance of $10$ units from $Q$, to…

Three points $P$, $Q$, and $R$ are located on the number line. It is known that:

  • Point $Q$ is the opposite of $-6$.

  • Point $P$ is at a distance of $10$ units from $Q$, to the left.

  • Point $R$ satisfies $|R| = |P| + |Q|$.

Calculate the values of $P$, $Q$, and $R$. Represent all possible positions of $R$ on the line and explain which of them is furthest from the midpoint between $P$ and $Q$.

You can do it on paper and send a photo with your answer.

Solve
Practice★★★Not started
An explorer is in a network of underground caves represented on a horizontal number line. The origin $0$ is the cave entrance. We know that the explorer has made the…

An explorer is in a network of underground caves represented on a horizontal number line. The origin $0$ is the cave entrance. We know that the explorer has made the following successive movements:

  1. Starts at an unknown point $x$.

  2. Moves forward $+12$ units.

  3. Moves back twice their initial position $x$ (that is, $2x$ units to the left).

  4. Moves forward the opposite of $-5$.

If they finally end up at point $-3$, represent the situation on the number line (draw the line and the movements yourself) and determine, with reasoning, the value of the starting point $x$.

Solve

Summary

Back to the beginning: the young man leaves Zócalo, goes $3$ stations west ($-3$) and $2$ east ($+2$). He ends up at $-3 + 2 = -1$, which is $|-1| = 1$ station from where he started.

See all the exercises in this section