PSLE
At first, a box contained 12 brown marbles and some red beads. After some brown marbles were added, 25 of the marbles were red. After 20 black marbles were added to the box and now, 27 of the beads were red. What was the number of brown marbles added?
|
Red marbles |
Brown marbles |
Black marbles |
Total |
Before |
2 u |
12 |
0 |
|
Change 1 |
|
+ ? |
|
+ ? |
After 1 |
2 u |
3 u |
0 |
5 u |
Change 2 |
|
|
+ 20 |
+ 2 u |
After 2 |
2 u |
3 u |
2 u |
7 u |
Some brown marbles were added at first. However, when 20 black marbles were added, the number of brown marbles remains unchanged.
Number of black marbles added
= 7 u - 5 u
= 2 u
2 u = 20
1 u = 20 ÷ 2 = 10
Number of brown marbles added
= 3 u - 12
= 3 x 10 - 12
= 30 - 12
= 18
Answer(s): 18