PSLE
At first, a box contained 12 silver marbles and some white beads. After some silver marbles were added, 37 of the marbles were white. After 78 brown marbles were added to the box and now, 313 of the beads were white. What was the number of silver marbles added?
|
White marbles |
Silver marbles |
Brown marbles |
Total |
Before |
3 u |
12 |
0 |
|
Change 1 |
|
+ ? |
|
+ ? |
After 1 |
3 u |
4 u |
0 |
7 u |
Change 2 |
|
|
+ 78 |
+ 6 u |
After 2 |
3 u |
4 u |
6 u |
13 u |
Some silver marbles were added at first. However, when 78 brown marbles were added, the number of silver marbles remains unchanged.
Number of brown marbles added
= 13 u - 7 u
= 6 u
6 u = 78
1 u = 78 ÷ 6 = 13
Number of silver marbles added
= 4 u - 12
= 4 x 13 - 12
= 52 - 12
= 40
Answer(s): 40