Twelve minutes ago, 70% of the children in a hall were boys. 102 children left the hall. As a result, the number of boys decreased by 30% and the number of girls decreased by 70%. How many children are in the hall at first?
| |
Boys |
Girls |
Total |
| Before |
10 u |
3 u |
13 u |
| Change |
- 3 u |
- 2.1 u |
- 5.1 u |
| After |
7 u |
0.9 u |
7.9 u |
70% =
70100 =
710Number of boys who left the hall
= 30% x 10 u
=
30100 x 10 u
= 3 u
Number of girls who left the hall
= 70% x 3 u
=
70100 x 3 u
= 2.1 u
Total number of children who left the hall
= 3 u + 2.1 u
= 5.1 u
5.1 u = 102
1 u = 102 ÷ 5.1 = 20
Number of children in the hall at first
= 10 u + 3 u
= 13 u
= 13 x 20
= 260
Answer(s): 260
