Nineteen minutes ago, 60% of the pupils in a canteen were boys. 39 pupils left the canteen. As a result, the number of boys decreased by 20% and the number of girls decreased by 80%. How many pupils are in the canteen at first?
| |
Boys |
Girls |
Total |
| Before |
5 u |
2 u |
7 u |
| Change |
- 1 u |
- 1.6 u |
- 2.6 u |
| After |
4 u |
0.4 u |
4.4 u |
60% =
60100 =
35Number of boys who left the canteen
= 20% x 5 u
=
20100 x 5 u
= 1 u
Number of girls who left the canteen
= 80% x 2 u
=
80100 x 2 u
= 1.6 u
Total number of pupils who left the canteen
= 1 u + 1.6 u
= 2.6 u
2.6 u = 39
1 u = 39 ÷ 2.6 = 15
Number of pupils in the canteen at first
= 5 u + 2 u
= 7 u
= 7 x 15
= 105
Answer(s): 105
