155 pupils went for a singing competition and 77 of them achieved Silver certificates.
35 of the girls and
13 of the boys achieved Silver certificates. How many girls did not achieve Silver certificates?
Boys |
Girls |
5 u |
3 p |
Achieved Silver |
Did not achieve Silver |
Achieved Silver |
Did not achieve Silver |
3 u |
2 u |
1 p |
2 p |
Number of pupils who did not achieve Silver certificates
= 155 - 77
= 78
3 u + 1 p = 77
1 p = 77 - 3 u --- (1)
2 u + 2 p = 78
2 p = 78 - 2 u --- (2)
Make p the same.
(1)
x22 p = 154 - 6 u --- (3)
(2) = (3)
78 - 2 u = 154 - 6 u
6 u - 2 u = 154 - 78
4 u = 76
1 u = 76 ÷ 4 = 19
Number of boys who achieved Silver certificates
= 3 u
= 3 x 19
= 57
Number of girls who achieved Silver certificates
= 77 - 57
= 20
Answer(s): 20