PSLE At first, a box contained 56 red marbles and some black beads. After some red marbles were removed,
58 of the marbles were black. After 55 white marbles were added to the box and now,
513 of the beads were black. What was the number of red marbles removed?
|
Black marbles |
Red marbles |
White marbles |
Total |
Before |
5 u |
56 |
0 |
|
Change 1 |
|
- ? |
|
+ ? |
After 1 |
5 u |
3 u |
0 |
8 u |
Change 2 |
|
|
+ 55 |
+ 5 u |
After 2 |
5 u |
3 u |
5 u |
13 u |
Some red marbles were removed at first. However, when 55 white marbles were added, the number of red marbles remains unchanged.
Number of white marbles added
= 13 u - 8 u
= 5 u
5 u = 55
1 u = 55 ÷ 5 = 11
Number of red marbles removed
= 56 - 3 u
= 56 - 3 x 11
= 56 - 33
= 23
Answer(s): 23