PSLE A box contained grey balls and black balls. 40% of the balls were black. After some red balls were added to the box, 10% of the balls were black. What percentage of the balls in the box were red?
|
Black |
Grey |
Red |
Total |
Before |
2 u |
3 u |
|
5 u |
Change |
|
|
+ ? |
|
After |
10% |
15% |
|
100% |
40% =
40100 =
25 The number of black balls remains unchanged.
2 u → 10%
1 u → 10% ÷ 2 = 5%
3 u → 3 x 5 = 15%
Percentage of the balls in the box that were red
= 100% - 10% - 15%
= 75%
Answer(s): 75%