PSLE A box contained red balls and grey balls. 30% of the balls were grey. After some black balls were added to the box, 15% of the balls were grey. What percentage of the balls in the box were black?
|
Grey |
Red |
Black |
Total |
Before |
3 u |
7 u |
|
10 u |
Change |
|
|
+ ? |
|
After |
15% |
35% |
|
100% |
30% =
30100 =
310 The number of grey balls remains unchanged.
3 u → 15%
1 u → 15% ÷ 3 = 5%
7 u → 7 x 5 = 35%
Percentage of the balls in the box that were black
= 100% - 15% - 35%
= 50%
Answer(s): 50%