PSLE A box contained purple balls and black balls. 30% of the balls were black. After some red balls were added to the box, 27% of the balls were black. What percentage of the balls in the box were red?
|
Black |
Purple |
Red |
Total |
Before |
3 u |
7 u |
|
10 u |
Change |
|
|
+ ? |
|
After |
27% |
63% |
|
100% |
30% =
30100 =
310 The number of black balls remains unchanged.
3 u → 27%
1 u → 27% ÷ 3 = 9%
7 u → 7 x 9 = 63%
Percentage of the balls in the box that were red
= 100% - 27% - 63%
= 10%
Answer(s): 10%