21 Primary 3 students and 18 of Primary 4 students went on a school excursion. The number of Primary 4 girls was 4 times the number of Primary 3 girls, and there were 12 more Primary 3 boys than Primary 4 boys. How many less Primary 4 boys than Primary 4 girls went on the school excursion?
| Primary 3 |
Primary 4 |
| 21 |
18 |
| Girls |
Boys |
Girls |
Boys |
| 1 u |
1 p + 12 |
4 u |
1 p |
Total number of students in Primary 3 = 1 u + 1 p + 12
1 u + 1 p + 12 = 21
1 u + 1 p = 21 - 12
1 u + 1 p = 9 --- (1)
Total number of students in Primary 4 = 4 u + 1 p
4 u + 1 p = 18 --- (2)
(2) - (1)
(4 u + 1 p) - (1 u + 1 p) = 18 - 9
4 u - 1 u = 9
3 u = 9
1 u = 9 ÷ 3 = 3
Number of girls in Primary 4
= 4 u
= 4 x 3
= 12
Number of boys in Primary 4
= 1 p
= 18 - 4 u
= 18 - 12
= 6
Number of less boys than girls in Primary 4
= 12 - 6
= 6
Answer(s): 6
