 Rewriting subtraction problems

Lesson

We've already looked at subtraction, which is what we use to find the difference between to numbers.

Now we are going to look at another way to find the difference between two numbers that uses the distributive property. For example, let's say we wanted to find $72-48$7248.

1. Find the highest common factor (HCF) between the two numbers.

The factors of $48$48 are:

$1,2,3,4,6,8,12,16,24,48$1,2,3,4,6,8,12,16,24,48

The factors of $72$72 are:

$1,2,3,4,6,8,9,12,18,24,36,72$1,2,3,4,6,8,9,12,18,24,36,72

The numbers that appear in both factor lists are:

$1,2,3,4,6,8,12,24$1,2,3,4,6,8,12,24

The largest number in this list is the HCF, $24$24.

2. Rewrite the expression as an equivalent multiplication by using the distributive property.

$48=24\times2$48=24×2

$72=24\times3$72=24×3

$72-48=24\times\left(3-2\right)$7248=24×(32)

$24\times\left(3-2\right)=24\times1$24×(32)=24×1

$24\times1=24$24×1=24

So, $72-48=24$7248=24.

And there you go! Another way to find the difference between to numbers.

Now let's practice it.

Practice questions

Question 1

Consider the difference $96-80$9680 :

1. Find the HCF of $96$96 and $80$80.

2. Complete the gaps such that $96-80$9680 is rewritten as an equivalent multiplication using the distributive property.

 $96-80$96−80 $=$= $16\times\left(\editable{}-5\right)$16×(−5) $=$= $16\times\editable{}$16×

Question 2

Consider $11\left(7-3\right)$11(73).

1. Using the distributive law, complete the gap so that $11\left(7-3\right)$11(73) is rewritten as the difference of two integers.

$11\left(7-3\right)=77-\editable{}$11(73)=77

Question 3

Hermione and Yuri both earn $\$1111 per hour in their casual job. In a day where one works for $7$7 hours and the other works for $2$2 hours, complete the number sentence that can be used to evaluate the difference in their wages (with the difference expressed as a positive quantity).

1. Difference in wages = $\editable{}\left(\editable{}-\editable{}\right)$()

Outcomes

NA3-7

Generalise the properties of addition and subtraction with whole numbers