PSLE At first, a box contained 79 blue marbles and some red beads. After some blue marbles were removed,
37 of the marbles were red. After 18 black marbles were added to the box and now,
313 of the beads were red. What was the number of blue marbles removed?
|
Red marbles |
Blue marbles |
Black marbles |
Total |
Before |
3 u |
79 |
0 |
|
Change 1 |
|
- ? |
|
+ ? |
After 1 |
3 u |
4 u |
0 |
7 u |
Change 2 |
|
|
+ 18 |
+ 6 u |
After 2 |
3 u |
4 u |
6 u |
13 u |
Some blue marbles were removed at first. However, when 18 black marbles were added, the number of blue marbles remains unchanged.
Number of black marbles added
= 13 u - 7 u
= 6 u
6 u = 18
1 u = 18 ÷ 6 = 3
Number of blue marbles removed
= 79 - 4 u
= 79 - 4 x 3
= 79 - 12
= 67
Answer(s): 67