PSLE Hilda had a box of blue beads and black beads in the ratio 13 : 7. She removed an equal number of blue beads and black beads from the box. The ratio of the number of blue beads and black beads left in the box became 9 : 4. What percentage of the beads were left in the box?
|
Blue beads |
Black beads |
Difference |
Total |
Before |
13x5 = 65 u |
7x5 = 35 u |
6x5 = 30 u |
20x5 = 100 u |
Change |
- 11 u |
- 11 u |
|
|
After |
9x6 = 54 u |
4x6 = 24 u |
5x6 = 30 u |
13x6 = 78 u |
When Hilda removed an equal number of blue beads and black beads, the difference between the number of blue beads and black beads at first and in the end remains the same.
LCM of 6 and 5 is 30.
Percentage of the beads left in the box
=
78100 x 100%
= 3950 x 100%
= 78%
Answer: 78%