1. 1 5 = 2 a Cross multiplying is a strategy for finding
the missing part of a
set of equivalent
fractions.
The letter a is supposed
to represent the number you don’t know yet. It is called a variable. 1 5 = 2 a

2. 1 5 = 2 a 2 x 5 = 1 x a = 1 x a 10 The letter a is supposed
Use that brain in your head:
If 10 is 1 times some number,
what is that number?
The letter a is supposed
To represent the number
You don’t know yet. It is called a variable.
Cross multiplying is a
strategy for finding
the missing part of a
set of equivalent
fractions. 1 5 = 2 a
2 x 5
= 1 x a
= 1 x a 10

3. 1 5 = 2 a 10 Yes. Since 10 = 1 x 10, the variable a in this
case is 10. 1 5 = 2 a 10
2 x 5
= 1 x a
= 1 x a 10

4. If 84 is three times some number, then
84 ÷ 3 will reveal
the missing amount. 3 12 = 7 a
7 x 12
= 3 x a 84
= 3 x a

5. If 84 is three times some number, then
84 ÷ 3 will reveal
the missing amount. 2 8
8 4 3 6 3 12 2 4 = 2 4 7 a
7 x 12
= 3 x a 84
= 3 x a

6. If 84 is three times some number, then
84 ÷ 3 will reveal
the missing amount. 2 8
8 4 3 6 3 12 2 4 = 2 4 7 a 28
7 x 12
= 3 x a 84
= 3 x a

7. (6 x 2) +3=15 6 6 15 b __ __ 25
1500 = 3 25
100 15
25 x b
15 x 100 =
1,500 ÷ 25 = b 6 = b

8. 66.6 6 6 6 8 n 12
8 0 0 = 72 12
100 8 72
800
12 n = 8 n
800 /12 =
7 2 n
66.6 =

9. A LOT OF STEPS!

10. Soon you will
know how to solve
even harder problems!