PSLE Jean had a box of black balls and brown balls in the ratio 17 : 8. She removed an equal number of black balls and brown balls from the box. The ratio of the number of black balls and brown balls left in the box became 7 : 3. What percentage of the balls were left in the box?
|
Black balls |
Brown balls |
Difference |
Total |
Before |
17x4 = 68 u |
8x4 = 32 u |
9x4 = 36 u |
25x4 = 100 u |
Change |
- 5 u |
- 5 u |
|
|
After |
7x9 = 63 u |
3x9 = 27 u |
4x9 = 36 u |
10x9 = 90 u |
When Jean removed an equal number of black balls and brown balls, the difference between the number of black balls and brown balls at first and in the end remains the same.
LCM of 9 and 4 is 36.
Percentage of the balls left in the box
=
90100 x 100%
= 910 x 100%
= 90%
Answer: 90%