Section D: Ratio Tables and Multiplication Set 2
Because multiplication and division are related, ratio tables can be used to solve both kinds of problems.
Can you use a ratio table to solve a division problem? Here is one way .
252 ÷ 12 k
1
12
10
120
20
240
21
252
2
42
12
252
So… 252 ÷ 12 = 21
Now let’s use a ratio table to multiply 12 × 21.
1
21
10
210
So… 12 × 21 = 252
1. Complete each division problem.
a) How many 15s are there in 90?
1
15
b) How many 20s are there in 660?
c) How many 16s are there in 256?
d) How many 18s are there in 378?
Book 4: Multiplication and Division 15
Section G: A Model for Division
Set 1
Let’s try another example: 432 ÷ 18
10 groups of 18 = 180.
If you subtract from 432
then 252 are left.
10 groups of 18 = 180.
If you subtract from 252
then 72 are left.
2 groups of 18 = 36.
If you subtract from 72
then 36 are left.
2 groups of 18 = 36.
If you subtract from 36
then 0 are left.
432
Groups of 18
-180
252
10
- 180
72
10
- 36
36
2
- 36
0
2
HINT: Try to use easier groups that
you can multiply quickly in your
head, like groups of 10 or 20. Also,
you can use the “half of” strategy we
used in ratio tables. For example,
if 10 groups is 180, then 5 groups
would be 90.
24 Groups of 18 in 432
You can be as creative as you want in making groups – just like you are when you use a ratio table – by
using numbers that you can easily calculate in your head. One more example: 5124 ÷ 42 = ? Here are two
ways you might find the quotient.
5124
5124
Groups of 42
Groups of 42
-1680
3444
40
-4200
924
100
- 3360
84
80
- 840
84
20
- 84
0
2
- 84
0
2
122
122
122 groups of 42 in 5124
30 Book 4: Multiplication and Division