PSLE At first, a box contained 72 blue balls and some purple beads. After some blue balls were removed,
47 of the balls were purple. After 12 grey balls were added to the box and now,
413 of the beads were purple. What was the number of blue balls removed?
|
Purple balls |
Blue balls |
Grey balls |
Total |
Before |
4 u |
72 |
0 |
|
Change 1 |
|
- ? |
|
+ ? |
After 1 |
4 u |
3 u |
0 |
7 u |
Change 2 |
|
|
+ 12 |
+ 6 u |
After 2 |
4 u |
3 u |
6 u |
13 u |
Some blue balls were removed at first. However, when 12 grey balls were added, the number of blue balls remains unchanged.
Number of grey balls added
= 13 u - 7 u
= 6 u
6 u = 12
1 u = 12 ÷ 6 = 2
Number of blue balls removed
= 72 - 3 u
= 72 - 3 x 2
= 72 - 6
= 66
Answer(s): 66