PSLE A box contained yellow marbles and red marbles. 40% of the marbles were red. After some black marbles were added to the box, 28% of the marbles were red. What percentage of the marbles in the box were black?
|
Red |
Yellow |
Black |
Total |
Before |
2 u |
3 u |
|
5 u |
Change |
|
|
+ ? |
|
After |
28% |
42% |
|
100% |
40% =
40100 =
25 The number of red marbles remains unchanged.
2 u → 28%
1 u → 28% ÷ 2 = 14%
3 u → 3 x 14 = 42%
Percentage of the marbles in the box that were black
= 100% - 28% - 42%
= 30%
Answer(s): 30%