Seven minutes ago, 60% of the students in a hall were boys. 72 students left the hall. As a result, the number of boys decreased by 40% and the number of girls decreased by 80%. How many students are in the hall at first?
| |
Boys |
Girls |
Total |
| Before |
5 u |
2 u |
7 u |
| Change |
- 2 u |
- 1.6 u |
- 3.6 u |
| After |
3 u |
0.4 u |
3.4 u |
60% =
60100 =
35Number of boys who left the hall
= 40% x 5 u
=
40100 x 5 u
= 2 u
Number of girls who left the hall
= 80% x 2 u
=
80100 x 2 u
= 1.6 u
Total number of students who left the hall
= 2 u + 1.6 u
= 3.6 u
3.6 u = 72
1 u = 72 ÷ 3.6 = 20
Number of students in the hall at first
= 5 u + 2 u
= 7 u
= 7 x 20
= 140
Answer(s): 140
