There were twice as many boys as girls at a conference. After 21 girls left the conference, there were five times as many boys as girls who remained behind. How many boys were there at the conference?
| |
Boys |
Girls |
| Before |
2x5 =
10 u |
1x5 =
5 u |
| Change |
|
- 21 |
| After |
5x2 =
10 u |
1x2 =
2 u |
The number of boys remained unchanged. Make the number of boys the same. LCM of 2 and 5 is 10.
Decrease in the number of girls
= 5 u - 2 u
= 3 u
3 u = 21
1 u = 21 ÷ 3 = 7
Number of boys
= 10 u
= 10 x 7
= 70
Answer(s): 70
