Eleven minutes ago, 75% of the pupils in a canteen were girls. 18 pupils left the canteen. As a result, the number of girls decreased by 25% and the number of boys decreased by 80%. How many pupils are in the canteen at first?
| |
Girls |
Boys |
Total |
| Before |
4 u |
1 u |
5 u |
| Change |
- 1 u |
- 0.8 u |
- 1.8 u |
| After |
3 u |
0.2 u |
3.2 u |
75% =
75100 =
34Number of girls who left the canteen
= 25% x 4 u
=
25100 x 4 u
= 1 u
Number of boys who left the canteen
= 80% x 1 u
=
80100 x 1 u
= 0.8 u
Total number of pupils who left the canteen
= 1 u + 0.8 u
= 1.8 u
1.8 u = 18
1 u = 18 ÷ 1.8 = 10
Number of pupils in the canteen at first
= 4 u + 1 u
= 5 u
= 5 x 10
= 50
Answer(s): 50
