PSLE At first, a container contained 81 black beads and some blue beads. After some black beads were removed,
57 of the beads were blue. After 30 yellow beads were added to the container and now,
512 of the beads were blue. What was the number of black beads removed?
|
Blue beads |
Black beads |
Yellow beads |
Total |
Before |
5 u |
81 |
0 |
|
Change 1 |
|
- ? |
|
+ ? |
After 1 |
5 u |
2 u |
0 |
7 u |
Change 2 |
|
|
+ 30 |
+ 5 u |
After 2 |
5 u |
2 u |
5 u |
12 u |
Some black beads were removed at first. However, when 30 yellow beads were added, the number of black beads remains unchanged.
Number of yellow beads added
= 12 u - 7 u
= 5 u
5 u = 30
1 u = 30 ÷ 5 = 6
Number of black beads removed
= 81 - 2 u
= 81 - 2 x 6
= 81 - 12
= 69
Answer(s): 69