28 Primary 2 pupils and 20 of Primary 3 pupils went on a school camp. The number of Primary 3 girls was 4 times the number of Primary 2 girls, and there were 20 less Primary 3 boys than Primary 2 boys. How many less Primary 3 boys than Primary 3 girls went on the school camp?
| Primary 2 |
Primary 3 |
| 28 |
20 |
| Girls |
Boys |
Girls |
Boys |
| 1 u |
1 p + 20 |
4 u |
1 p |
Total number of pupils in Primary 2 = 1 u + 1 p + 20
1 u + 1 p + 20 = 28
1 u + 1 p = 28 - 20
1 u + 1 p = 8 --- (1)
Total number of pupils in Primary 3 = 4 u + 1 p
4 u + 1 p = 20 --- (2)
(2) - (1)
(4 u + 1 p) - (1 u + 1 p) = 20 - 8
4 u - 1 u = 12
3 u = 12
1 u = 12 ÷ 3 = 4
Number of girls in Primary 3
= 4 u
= 4 x 4
= 16
Number of boys in Primary 3
= 1 p
= 20 - 4 u
= 20 - 16
= 4
Number of less boys than girls in Primary 3
= 16 - 4
= 12
Answer(s): 12
