31 Primary 5 pupils and 23 of Primary 6 pupils went on a school excursion. The number of Primary 6 boys was 3 times the number of Primary 5 boys, and there were 18 less Primary 6 girls than Primary 5 girls. How many less Primary 6 girls than Primary 6 boys went on the school excursion?
| Primary 5 |
Primary 6 |
| 31 |
23 |
| Boys |
Girls |
Boys |
Girls |
| 1 u |
1 p + 18 |
3 u |
1 p |
Total number of pupils in Primary 5 = 1 u + 1 p + 18
1 u + 1 p + 18 = 31
1 u + 1 p = 31 - 18
1 u + 1 p = 13 --- (1)
Total number of pupils in Primary 6 = 3 u + 1 p
3 u + 1 p = 23 --- (2)
(2) - (1)
(3 u + 1 p) - (1 u + 1 p) = 23 - 13
3 u - 1 u = 10
2 u = 10
1 u = 10 ÷ 2 = 5
Number of boys in Primary 6
= 3 u
= 3 x 5
= 15
Number of girls in Primary 6
= 1 p
= 23 - 3 u
= 23 - 15
= 8
Number of less girls than boys in Primary 6
= 15 - 8
= 7
Answer(s): 7
