25 Primary 4 pupils and 21 of Primary 5 pupils went on a school oversea trip. The number of Primary 5 girls was 4 times the number of Primary 4 girls, and there were 13 less Primary 5 boys than Primary 4 boys. How many less Primary 5 boys than Primary 5 girls went on the school oversea trip?
| Primary 4 |
Primary 5 |
| 25 |
21 |
| Girls |
Boys |
Girls |
Boys |
| 1 u |
1 p + 13 |
4 u |
1 p |
Total number of pupils in Primary 4 = 1 u + 1 p + 13
1 u + 1 p + 13 = 25
1 u + 1 p = 25 - 13
1 u + 1 p = 12 --- (1)
Total number of pupils in Primary 5 = 4 u + 1 p
4 u + 1 p = 21 --- (2)
(2) - (1)
(4 u + 1 p) - (1 u + 1 p) = 21 - 12
4 u - 1 u = 9
3 u = 9
1 u = 9 ÷ 3 = 3
Number of girls in Primary 5
= 4 u
= 4 x 3
= 12
Number of boys in Primary 5
= 1 p
= 21 - 4 u
= 21 - 12
= 9
Number of less boys than girls in Primary 5
= 12 - 9
= 3
Answer(s): 3
