PSLE Ivory had a box of grey balls and gold balls in the ratio 13 : 7. She removed an equal number of grey balls and gold balls from the box. The ratio of the number of grey balls and gold balls left in the box became 7 : 1. What percentage of the balls were left in the box?
|
Grey balls |
Gold balls |
Difference |
Total |
Before |
13x1 = 13 u |
7x1 = 7 u |
6x1 = 6 u |
20x1 = 20 u |
Change |
- 6 u |
- 6 u |
|
|
After |
7x1 = 7 u |
1x1 = 1 u |
6x1 = 6 u |
8x1 = 8 u |
When Ivory removed an equal number of grey balls and gold balls, the difference between the number of grey balls and gold balls at first and in the end remains the same.
LCM of 6 and 6 is 6.
Percentage of the balls left in the box
=
820 x 100%
= 25 x 100%
= 40%
Answer: 40%