PSLE At first, a container contained 56 yellow balls and some grey beads. After some yellow balls were removed,
57 of the balls were grey. After 20 red balls were added to the container and now,
512 of the beads were grey. What was the number of yellow balls removed?
|
Grey balls |
Yellow balls |
Red balls |
Total |
Before |
5 u |
56 |
0 |
|
Change 1 |
|
- ? |
|
+ ? |
After 1 |
5 u |
2 u |
0 |
7 u |
Change 2 |
|
|
+ 20 |
+ 5 u |
After 2 |
5 u |
2 u |
5 u |
12 u |
Some yellow balls were removed at first. However, when 20 red balls were added, the number of yellow balls remains unchanged.
Number of red balls added
= 12 u - 7 u
= 5 u
5 u = 20
1 u = 20 ÷ 5 = 4
Number of yellow balls removed
= 56 - 2 u
= 56 - 2 x 4
= 56 - 8
= 48
Answer(s): 48