21 Primary 3 pupils and 12 of Primary 4 pupils went on a school trip. The number of Primary 4 boys was 4 times the number of Primary 3 boys, and there were 15 more Primary 3 girls than Primary 4 girls. How many more Primary 4 boys than Primary 4 girls went on the school trip?
| Primary 3 |
Primary 4 |
| 21 |
12 |
| Boys |
Girls |
Boys |
Girls |
| 1 u |
1 p + 15 |
4 u |
1 p |
Total number of pupils in Primary 3 = 1 u + 1 p + 15
1 u + 1 p + 15 = 21
1 u + 1 p = 21 - 15
1 u + 1 p = 6 --- (1)
Total number of pupils in Primary 4 = 4 u + 1 p
4 u + 1 p = 12 --- (2)
(2) - (1)
(4 u + 1 p) - (1 u + 1 p) = 12 - 6
4 u - 1 u = 6
3 u = 6
1 u = 6 ÷ 3 = 2
Number of boys in Primary 4
= 4 u
= 4 x 2
= 8
Number of girls in Primary 4
= 1 p
= 12 - 4 u
= 12 - 8
= 4
Number of more boys than girls in Primary 4
= 8 - 4
= 4
Answer(s): 4
