PSLE At first, a box contained 50 purple marbles and some blue beads. After some purple marbles were removed,
57 of the marbles were blue. After 16 black marbles were added to the box and now,
511 of the beads were blue. What was the number of purple marbles removed?
|
Blue marbles |
Purple marbles |
Black marbles |
Total |
Before |
5 u |
50 |
0 |
|
Change 1 |
|
- ? |
|
+ ? |
After 1 |
5 u |
2 u |
0 |
7 u |
Change 2 |
|
|
+ 16 |
+ 4 u |
After 2 |
5 u |
2 u |
4 u |
11 u |
Some purple marbles were removed at first. However, when 16 black marbles were added, the number of purple marbles remains unchanged.
Number of black marbles added
= 11 u - 7 u
= 4 u
4 u = 16
1 u = 16 ÷ 4 = 4
Number of purple marbles removed
= 50 - 2 u
= 50 - 2 x 4
= 50 - 8
= 42
Answer(s): 42