21 Primary 5 students and 18 of Primary 6 students went on a school camp. The number of Primary 6 girls was 3 times the number of Primary 5 girls, and there were 13 less Primary 6 boys than Primary 5 boys. How many less Primary 6 boys than Primary 6 girls went on the school camp?
| Primary 5 |
Primary 6 |
| 21 |
18 |
| Girls |
Boys |
Girls |
Boys |
| 1 u |
1 p + 13 |
3 u |
1 p |
Total number of students in Primary 5 = 1 u + 1 p + 13
1 u + 1 p + 13 = 21
1 u + 1 p = 21 - 13
1 u + 1 p = 8 --- (1)
Total number of students in Primary 6 = 3 u + 1 p
3 u + 1 p = 18 --- (2)
(2) - (1)
(3 u + 1 p) - (1 u + 1 p) = 18 - 8
3 u - 1 u = 10
2 u = 10
1 u = 10 ÷ 2 = 5
Number of girls in Primary 6
= 3 u
= 3 x 5
= 15
Number of boys in Primary 6
= 1 p
= 18 - 3 u
= 18 - 15
= 3
Number of less boys than girls in Primary 6
= 15 - 3
= 12
Answer(s): 12
