31 Primary 4 students and 21 of Primary 5 students went on a school oversea trip. The number of Primary 5 boys was 3 times the number of Primary 4 boys, and there were 20 less Primary 5 girls than Primary 4 girls. How many less Primary 5 girls than Primary 5 boys went on the school oversea trip?
Primary 4 |
Primary 5 |
31 |
21 |
Boys |
Girls |
Boys |
Girls |
1 u |
1 p + 20 |
3 u |
1 p |
Total number of students in Primary 4 = 1 u + 1 p + 20
1 u + 1 p + 20 = 31
1 u + 1 p = 31 - 20
1 u + 1 p = 11 --- (1)
Total number of students in Primary 5 = 3 u + 1 p
3 u + 1 p = 21 --- (2)
(2) - (1)
(3 u + 1 p) - (1 u + 1 p) = 21 - 11
3 u - 1 u = 10
2 u = 10
1 u = 10 ÷ 2 = 5
Number of boys in Primary 5
= 3 u
= 3 x 5
= 15
Number of girls in Primary 5
= 1 p
= 21 - 3 u
= 21 - 15
= 6
Number of less girls than boys in Primary 5
= 15 - 6
= 9
Answer(s): 9