How to Read a Number line

Hey guys! Welcome to this video on how to use a number line!

Using a number line can be useful when you are adding and subtracting numbers.

Let’s take a look at a problem:

Lacy has 9 pieces of gum. She gave two pieces to her friend Martha in first period. In second period, she gave one piece each to Jonathan, and Casey. In her last period she gave a piece to each of her three lab partners. When Lacy’s mom picked her up from school she gave her a new pack of gum with ten pieces in it. How many pieces of gum does Lacy now have left?

Alright, so let’s start by first drawing our number line.

Now, let’s read back through the problem and follow what happens with the gum on our number line. When we start, Lacy has 9 pieces of gum, so we’re over here at 9.

And then she gave 2 pieces to her friend Martha in first period. So we go back on our number line. She gave them away, so now she is missing 2 pieces. So we go back 2 spots, so now she has 7.

Well, what happens next? In second period she gave 1 piece each to Jonathan and Casey, so she gave 1 piece to Jonathan and 1 piece to Casey. She gave away 2 more pieces. So we gotta go to the left 2 more times. So now she’s at 5 pieces.

And then what happens? In her last period, she gave a piece to each of her 3 lab partners. So she gave 1 piece to 3 different people, so that’s minus 3 pieces of gum. So we go to the left 3 spots, so that puts us at 2.

Then what happens? When Lacey’s mom picked her up from school, she gave her a new pack of gum with 10 pieces in it. How many pieces does Lacey have left? Alright, so her mom gave her 10 new pieces so we’re adding 10 onto the 2 we have right here, so we need to go to the right 10 places on our number line. So that gets us all the way up to here at 12.

Alright, so at the end of the day, Lacey’s mom comes to the rescue and gives her 10 more pieces so she ends up starting with more pieces than she had at the beginning.

Number lines can be really useful to help you visualize the changes taking place, and to help you keep track of where you are at in your word problem.

I hope this video was helpful!

See you guys next time!

Practice Questions

Question #1:

 
Which scenario matches the number line below?
8 through 22 number line

Beth is selling bracelets at an art fair. She starts her day with nine bracelets, and then she sells four of them. Now she only has five more bracelets to sell.

Tony goes to the grocery store with nine dollars. He spends thirteen dollars for cereal and milk, and now he has four dollars left.

Tanya has thirteen dog treats in her pocket. She gives her puppy four of the treats, so now she has nine treats left.

John earns thirteen dollars mowing the neighbor’s lawn. On his way home, he spends nine dollars on a snack. Now John only has four dollars left.

Answer:

Tanya starts with thirteen treats in her pocket, and then gives her puppy four of them. This is represented on the number line as four jumps back to the left from the number thirteen, landing on the number nine. In other words, \(13-4=9\).

Question #2:

 
Which math sentence matches the number line below? Note that the original starting point is at zero.
Negative 7 to 7 number line

\(0+12-5=7\)
\(0-7+12=5\)
\(0+5-12=7\)
\(0-5+12=7\)
Answer:

Starting at 0, we move left (back) five jumps and land on -5. From -5, we then move to the right 12 jumps, landing on 7. Zero minus five, plus twelve, equals seven, which matches the number sentence \(0-5+12=7\).

Question #3:

 
Which number line correctly plots the point 1.5?

Red dot between negative 3 and negative 2 on a number line

Red dot between 1 and 2 on a number line

Red dot between -1 and 0 on the number line

Red dot between 2 and 3 on the number line

Answer:

Number line B shows the point 1.5 correctly plotted between 1 and 2.

Question #4:

 
Joey paints 11 picture frames blue, and 8 picture frames green. He paints a total of 19 picture frames. A number line is used to represent the total number of frames painted. Identify the error in the number line below.
Blue line going from 0 to 11 and green line going from 11 to 20 on number line

The green line is incorrect. It shows a jump of 9, but it should show a jump of 8.

The blue line is incorrect. It should show a jump of 12, not 11.

Both lines are incorrect.

The green line is incorrect. It should show a jump of 13, not 9.

Answer:

Joey painted 11 blue frames, so the blue line is correct in showing a jump of 11. He painted 8 frames green, so the green line should show a jump of 8, from 11 to 19. However, the green line is incorrect. The green line shows a jump of 9, landing on 20.

Question #5:

 
Fill in the missing value so that the number line matches the number sentence:
\(3+\text{___}=8\)
Line going from 0 to 8 on a number line

4

5

6

7

Answer:

The number line shows a starting point of 3, and then 5 jumps to the right, eventually landing on the number 8. The number line matches the number sentence \(3+5=8\), so the missing value is 5.

816439321029

 

by Mometrix Test Preparation | Last Updated: September 6, 2021