In February, the ratio of girls and boys in a school's Robotics Club was 3 : 5. In March, 39 new members joined the club. As a result, the ratio of girls to boys in the club became 5 : 4. There were 9 girls in the Robotics Club in February. How many of the new members were boys?
| |
Girls |
Boys |
| Before |
3 u |
5 u |
| Change |
+ 39 |
| After |
5 p |
4 p |
Number of girls at first = 3 u
3 u = 9
1 u = 9 ÷ 3 = 3
Total number of members at first
= 3 u + 5 u
= 8 u
= 8 x 3
= 24
Total number of members in the end
= 24 + 39
= 63
Total number of members in the end
= 5 p + 4 p
= 9 p
9 p = 63
1 p = 63 ÷ 9 = 7
Number of boys in the end
= 4 p
= 4 x 7
= 28
Number of boys at first
= 5 u
= 5 x 3
= 15
Number of new members who were boys
= 28 - 15
= 13
Answer(s): 13
