Risa and Opal had $159. Opal had $31 more than Risa. Risa spent 3 times as much as Opal and was left with
25 as much as Opal. How much did Risa spend?
| |
Make p the same
(1)x5 = (3) |
Risa
(1) |
Opal
(2) |
Make p the same
(2)x2 = (4) |
Total
|
Comparing Risa
and Opal at first |
|
|
$31 more |
|
$159 |
| Before |
$320 |
$64 |
$95 |
$190 |
|
| Change |
- 15 u |
- 3 u |
- 1 u |
- 2 u |
|
| After |
10 p |
2 p |
5 p |
10 p |
|
Amount that Risa had at first
= (159 - 31) ÷ 2
= 128 ÷ 2
= $64
Amount that Opal had at first
= 64 + 31
= $95
64 - 3 u = 2 p --- (1)
95 - 1 u = 5 p --- (2)
Make p the same.
(1)
x 5
320 - 15 u =
10 p --- (3)
(2)
x 2
190 - 2 u =
10 p --- (4)
(4) = (3)
190 - 2 u = 320 - 15 u
15 u - 2 u = 320 - 190
13 u = 130
1 u = 130 ÷ 13 = 10
Amount that Risa spent
= 3 u
= 3 x 10
= $30
Answer(s): $30
