36 Primary 4 pupils and 32 of Primary 5 pupils went on a school excursion. The number of Primary 5 girls was 3 times the number of Primary 4 girls, and there were 20 less Primary 5 boys than Primary 4 boys. How many less Primary 5 boys than Primary 5 girls went on the school excursion?
| Primary 4 |
Primary 5 |
| 36 |
32 |
| Girls |
Boys |
Girls |
Boys |
| 1 u |
1 p + 20 |
3 u |
1 p |
Total number of pupils in Primary 4 = 1 u + 1 p + 20
1 u + 1 p + 20 = 36
1 u + 1 p = 36 - 20
1 u + 1 p = 16 --- (1)
Total number of pupils in Primary 5 = 3 u + 1 p
3 u + 1 p = 32 --- (2)
(2) - (1)
(3 u + 1 p) - (1 u + 1 p) = 32 - 16
3 u - 1 u = 16
2 u = 16
1 u = 16 ÷ 2 = 8
Number of girls in Primary 5
= 3 u
= 3 x 8
= 24
Number of boys in Primary 5
= 1 p
= 32 - 3 u
= 32 - 24
= 8
Number of less boys than girls in Primary 5
= 24 - 8
= 16
Answer(s): 16
