Seven minutes ago, 60% of the students in a canteen were boys. 57 students left the canteen. As a result, the number of boys decreased by 40% and the number of girls decreased by 90%. How many students are in the canteen at first?
| |
Boys |
Girls |
Total |
| Before |
5 u |
2 u |
7 u |
| Change |
- 2 u |
- 1.8 u |
- 3.8 u |
| After |
3 u |
0.2 u |
3.2 u |
60% =
60100 =
35Number of boys who left the canteen
= 40% x 5 u
=
40100 x 5 u
= 2 u
Number of girls who left the canteen
= 90% x 2 u
=
90100 x 2 u
= 1.8 u
Total number of students who left the canteen
= 2 u + 1.8 u
= 3.8 u
3.8 u = 57
1 u = 57 ÷ 3.8 = 15
Number of students in the canteen at first
= 5 u + 2 u
= 7 u
= 7 x 15
= 105
Answer(s): 105
