Subtract Whole Numbers

1.3 Subtract Whole Numbers

The topics covered in this section are:

  1. Use subtraction notation
  2. Model subtraction of whole numbers
  3. Subtract whole numbers
  4. Translate word phrases to math notation
  5. Subtract whole numbers in applications

1.3.1 Use Subtraction Notation

Suppose there are seven bananas in a bowl. Elana uses three of them to make a smoothie. How many bananas are left in the bowl? To answer the question, we subtract three from seven. When we subtract, we take one number away from another to find the difference. The notation we use to subtract 3 from 7 is

7-3

We read 7-3 as seven minus three and the result is the difference of seven and three.

Subtraction Notation

To describe subtraction, we can use symbols and words.

OperationNotationExpressionRead asResult
Subtraction-7-3seven minus hreethe difference of 7 and 3

Example 1

Translate from math notation to words:

  • 8-1
  • 26-14

Solution

  • We read this as eight minus one. The result is the difference of eight and one.
  • We read this as twenty-six minus fourteen. The result is the difference of twenty-six and fourteen.

1.3.2 Model Subtraction of Whole Numbers

A model can help us visualize the process of subtraction much as it did with addition. Again, we will use base-10 blocks. Remember a block represents 1 and a rod represents 10. Let’s start by modeling the subtraction expression we just considered, 7-3.

We start by modeling the first number, 7.
Now take away the second number, 3. We'll circle 3 blocks to show that we are taking them away.
Count the number of blocks remaining.
There are 4 ones blocks left.We have shown that 7-3=4

MANIPULATIVE MATHEMATICS

Doing the Manipulative Mathematics activity Model Subtraction of Whole Numbers will help you develop a better understanding of subtracting whole numbers.

Example – 1

Model the subtraction: 8-2

Solution

8-2 means the difference of 8 and 2.
Model the first, 8.
Take away the second number, 2.
Count the number of blocks remaining.
There are 6 ones blocks left.We have show that 8-2=6.

Example – 2

Model the subtraction: 13-8

Solution

Model the first number, 13. We use 1 ten and 3 ones.
Take away the second number, 8. However, there are not 8 ones, so we will exchange the 1 ten for 10 ones.
Now we can take away 8 ones.
Count the blocks remaining.
There are five ones left.We have shown that 13-8=5.

As we did with addition, we can describe the models as ones blocks and tens rods, or we can simply say ones and tens.

Example – 3

Model the subtraction: 43-26

Solution

Because 43-26 means 43 take away 26, we begin by modeling the 43.

Now, we need to take away 26, which is 2 tens and 6 ones. We cannot take away 6 ones from 3 ones. So, we exchange 1 ten for 10 ones.

Now we can take away 2 tens and 6 ones.

Count the number of blocks remaining. There is 1 ten and 7 ones, which is 17.

1.3.3 Subtract Whole Numbers

Addition and subtraction are inverse operations. Addition undoes subtraction, and subtraction undoes addition.

We know 7-3=4 because 4+3=7. Knowing all the addition number facts will help with subtraction. Then we can check subtraction by adding. In the examples above, our subtractions can be checked by addition.

7-3=4 because 7+3=7

13-8=5 because 5+8=13

43-26=17 because 17+26=43

Example 1

Subtract and then check by adding:

  • 9-7
  • 8-3

Solution
9-7
Subtract 7 from 9.2
Check with addition.
2+7=9
8-3
Subtract 3 from 8.5
Check with addition.
5+3=8

To subtract numbers with more than one digit, it is usually easier to write the numbers vertically in columns just as we did for addition. Align the digits by place value, and then subtract each column starting with the ones and then working to the left.

Example 2

Subtract and the check by adding: 89-61.

Solution

Write the numbers so the ones and tens digits line up vertically.
Subtract the digits in each place value.
Subtract the ones: 9-1=8
Subtract the tens: 8-6=2
Check using addition.

When we modeled subtracting 26 from 43, we exchanged 1 ten for 10 ones. When we do this without the model, we say we borrow 1 from the tens place and add 10 to the ones place.

How to Find the Difference of Whole Numbers

  1. Write the numbers so each place value lines up vertically.
  2. Subtract the digits in each place value. Work from right to left starting with the ones place. If the digit on top is less than the digit below, borrow as needed.
  3. Continue subtracting each place value from right to left, borrowing if needed.
  4. Check by adding.

Example 3

Subtract: 43-26.

Solution
Write the numbers so each place value lines up vertically.
Subtract the ones. We cannot subtract 6 from 3, so we borrow 1 ten. This makes 3 tens and 13 ones.
We write these numbers above each place and cross out the original digits.
Now we can subtract the ones. 13-6=7. We write the 7 in the ones place in the difference.
Now we subtract the tens. 3-2=1. We write the 1 in the tens place in the difference.
Check by adding.
Our answer is correct.

Example 4

Subtract and then check by adding: 207-64.

Solution
Write the numbers so each place value lines up vertically.
Subtract the ones. 7-4=3.
Write the 3 in the ones place in the difference. Write the 3 in the ones place in the difference.
Subtract the tens. We cannot subtract 6 from 0 so we borrow 1 hundred and add 10 tens to the 0 tens we had. This makes a total of 10 tens. We write 10 above the tens place and cross out the 0. Then we cross out the 2 in the hundreds place and write 1 above it.
Now we subtract the tens. 10−6=4. We write the 4 in the tens place in the difference.
Finally, subtract the hundreds. There is no digit in the hundreds place in the bottom number so we can imagine a 0 in that place. Since 1−0=1, we write 1 in the hundreds place in the difference.
Check by adding.

Our answer is correct.

Example 5

Subtract and the check by adding: 910-586.

Solution
Write the numbers so each place value lines up vertically.
Subtract the ones. We cannot subtract 6 from 0, so we borrow 1 ten and add 10 ones to the 10 ones we had. This makes 10 ones. We write a 0 above the tens place and cross out the 1. We write the 10 above the ones place and cross out the 0. Now we can subtract the ones. 10−6=4.
Write the 4 in the ones place of the difference.
Subtract the tens. We cannot subtract 8 from 0, so we borrow 1 hundred and add 10 tens to the 0 tens we had, which gives us 10 tens. Write 8 above the hundreds place and cross out the 9. Write 10 above the tens place.
Now we can subtract the tens. 10−8=2.
Subtract the hundreds place. 8−5=3 Write the 3 in the hundreds place in the difference.
Check by adding.

Our answer is correct.

Example 6

Subtract and the check by adding: 2,162-479.

Solution
Write the numbers so each place values line up vertically.
Subtract the ones. Since we cannot subtract 9 from 2, borrow 1 ten and add 10 ones to the 2 ones to make 12 ones. Write 5 above the tens place and cross out the 6. Write 12 above the ones place and cross out the 2.
Now we can subtract the ones.12-9=3
Write 3 in the ones place in the difference.
Subtract the tens. Since we cannot subtract 7 from 5, borrow 1 hundred and add 10 tens to the 5 tens to make 15 tens. Write 0 above the hundreds place and cross out the 1. Write 15 above the tens place.
Now we can subtract the tens.15-7=8
Write 8 in the tens place in the difference.
Now we can subtract the hundreds.
Write 6 in the hundreds place in the difference.
Subtract the thousands. There is no digit in the thousands place of the bottom number, so we imagine a 0. 1−0=1. Write 1 in the thousands place of the difference.
Check by adding.
Our answer is correct.

1.3.4 Translate Word Phrases to Math Notation

As with addition, word phrases can tell us to operate on two numbers using subtraction. To translate from a word phrase to math notation, we look for key words that indicate subtraction. Some of the words that indicate subtraction are listed in the table below.

OperationWord PhraseExampleExpression
Subtractionminus5 minus 15-1
differencethe difference of 9 and 49-4
decreased by7 decreased by 37-3
less than5 less than 88-5
subtracted from1 subtracted from 66-1

Example 1

Translate and then simplify:

  • the difference of 13 and 8
  • subtract 24 from 43

1.3.4 Translate Word Phrases to Math Notation

As with addition, word phrases can tell us to operate on two numbers using subtraction. To translate from a word phrase to math notation, we look for key words that indicate subtraction. Some of the words that indicate subtraction are listed in the table below.

OperationWord PhraseExampleExpression
Subtractionminus5 minus 15-1
differencethe difference of 9 and 49-4
decreased by7 decreased by 37-3
less than5 less than 88-5
subtracted from1 subtracted from 66-1

Example 1

Translate and then simplify:

  • the difference of 13 and 8
  • subtract 24 from 43
Solution

The word difference tells us to subtract the two numbers. The numbers stay in the same order as in the phrase.

the difference of 13 and 8
Translate.13-8
Simplify.5

The words subtract from tells us to take the second number away from the first. We must be careful to get the order correct.

subtract 24 from 43
Translate43-24
Simplify19

1.3.5 Subtract Whole Numbers in Applications

To solve applications with subtraction, we will use the same plan that we used with addition. First, we need to determine what we are asked to find. Then we write a phrase that gives the information to find it. We translate the phrase into math notation and then simplify to get the answer. Finally, we write a sentence to answer the question, using the appropriate units.

Example 1

The temperature in Chicago one morning was 7373 degrees Fahrenheit. A cold front arrived and by noon the temperature was 2727 degrees Fahrenheit. What was the difference between the temperature in the morning and the temperature at noon?

Solution

We are asked to find the difference between the morning temperature and the noon temperature.

Write a phrase.the difference of 73 and 27
Translate to math notation. Difference tells us to subtract.73−27
Then we do the subtraction.
Write a sentence to answer the question.The difference in temperatures was 46 degrees Fahrenheit.

Example 2

A washing machine is on sale for $399.  Its regular price is $588. What is the difference between the regular price and the sale price?

1.3.5 Subtract Whole Numbers in Applications

To solve applications with subtraction, we will use the same plan that we used with addition. First, we need to determine what we are asked to find. Then we write a phrase that gives the information to find it. We translate the phrase into math notation and then simplify to get the answer. Finally, we write a sentence to answer the question, using the appropriate units.

Example 1

The temperature in Chicago one morning was 7373 degrees Fahrenheit. A cold front arrived and by noon the temperature was 2727 degrees Fahrenheit. What was the difference between the temperature in the morning and the temperature at noon?

Solution

We are asked to find the difference between the morning temperature and the noon temperature.

Write a phrase.the difference of 73 and 27
Translate to math notation. Difference tells us to subtract.73−27
Then we do the subtraction.
Write a sentence to answer the question.The difference in temperatures was 46 degrees Fahrenheit.

Example 2

A washing machine is on sale for $399.  Its regular price is $588. What is the difference between the regular price and the sale price?

Solution

We are asked to find the difference between the regular price and the sale price.

Write a phrase.the difference between 588 and 399
Translate to math notation.588-399
Subtract.
Write a sentence to answer the question.The difference between the regular price and the sale price is $189.
Licenses and Attributions

CC Licensed Content, Original

  • Revision and Adaptation. Provided by: Minute Math. License: CC BY 4.0

CC Licensed Content, Shared Previously

%d bloggers like this: