20 Primary 4 pupils and 17 of Primary 5 pupils went on a school oversea trip. The number of Primary 5 boys was 5 times the number of Primary 4 boys, and there were 15 more Primary 4 girls than Primary 5 girls. How many less Primary 5 girls than Primary 5 boys went on the school oversea trip?

Primary 4		Primary 5
20		17
Boys	Girls	Boys	Girls
1 u	1 p + 15	5  u	1 p

Total number of pupils in Primary 4 = 1 u + 1 p + 15

1 u + 1 p + 15 = 20
1 u + 1 p = 20 - 15
1 u + 1 p = 5 --- (1)

Total number of pupils in Primary 5 = 5 u + 1 p

5 u + 1 p = 17 --- (2)

(2) - (1)
(5 u + 1 p) - (1 u + 1 p) = 17 - 5
5 u - 1 u = 12
4 u = 12

1 u = 12 ÷ 4 = 3

Number of boys in Primary 5
= 5 u
= 5 x 3
= 15

Number of girls in Primary 5
= 1 p
= 17 - 5 u
= 17 - 15
= 2

Number of less girls than boys in Primary 5
= 15 - 2
= 13

Answer(s): 13