PSLE Barbara had a bag of black balls and red balls in the ratio 16 : 9. She removed an equal number of black balls and red balls from the bag. The ratio of the number of black balls and red balls left in the bag became 9 : 5. What percentage of the balls were left in the bag?
|
Black balls |
Red balls |
Difference |
Total |
Before |
16x4 = 64 u |
9x4 = 36 u |
7x4 = 28 u |
25x4 = 100 u |
Change |
- 1 u |
- 1 u |
|
|
After |
9x7 = 63 u |
5x7 = 35 u |
4x7 = 28 u |
14x7 = 98 u |
When Barbara removed an equal number of black balls and red balls, the difference between the number of black balls and red balls at first and in the end remains the same.
LCM of 7 and 4 is 28.
Percentage of the balls left in the bag
=
98100 x 100%
= 4950 x 100%
= 98%
Answer: 98%