There was an equal number of brown and black balls in a bag at first. After 30 black balls were taken out and 21 brown balls were added into the bag, there was
14 as many black balls as brown balls. Find the number of black balls in the bag at first.
| |
Brown balls |
Black balls |
| Before |
4 u - 21 |
1 u + 30 |
| Change |
+ 21 |
- 30 |
| After |
4 u |
1 u |
The number of brown and black balls in the bag is the same at first.
4 u - 21 = 1 u + 30
4 u - 1 u = 30 + 21
3 u = 51
1 u = 51 ÷ 3 = 17
Number of black balls at first
= 1 u + 30
= 17 + 30
= 47
Answer(s)47
