PSLE A box contained green balls and white balls. 30% of the balls were white. After some black balls were added to the box, 9% of the balls were white. What percentage of the balls in the box were black?
|
White |
Green |
Black |
Total |
Before |
3 u |
7 u |
|
10 u |
Change |
|
|
+ ? |
|
After |
9% |
21% |
|
100% |
30% =
30100 =
310 The number of white balls remains unchanged.
3 u → 9%
1 u → 9% ÷ 3 = 3%
7 u → 7 x 3 = 21%
Percentage of the balls in the box that were black
= 100% - 9% - 21%
= 70%
Answer(s): 70%