PSLE Emily had a box of black balls and silver balls in the ratio 17 : 8. She removed an equal number of black balls and silver balls from the box. The ratio of the number of black balls and silver balls left in the box became 9 : 1. What percentage of the balls were left in the box?
|
Black balls |
Silver balls |
Difference |
Total |
Before |
17x8 = 136 u |
8x8 = 64 u |
9x8 = 72 u |
25x8 = 200 u |
Change |
- 55 u |
- 55 u |
|
|
After |
9x9 = 81 u |
1x9 = 9 u |
8x9 = 72 u |
10x9 = 90 u |
When Emily removed an equal number of black balls and silver balls, the difference between the number of black balls and silver balls at first and in the end remains the same.
LCM of 9 and 8 is 72.
Percentage of the balls left in the box
=
90200 x 100%
= 920 x 100%
= 45%
Answer: 45%