There was an equal number of grey and silver marbles in a box at first. After 15 silver marbles were taken out and 21 grey marbles were added into the box, there was
17 as many silver marbles as grey marbles. Find the number of silver marbles in the box at first.
|
Grey marbles |
Silver marbles |
Before |
7 u - 21 |
1 u + 15 |
Change |
+ 21 |
- 15 |
After |
7 u |
1 u |
The number of grey and silver marbles in the box is the same at first.
7 u - 21 = 1 u + 15
7 u - 1 u = 15 + 21
6 u = 36
1 u = 36 ÷ 6 = 6
Number of silver marbles at first
= 1 u + 15
= 6 + 15
= 21
Answer(s)21