133 pupils went for a dancing competition and 63 of them achieved Silver certificates.
35 of the girls and
14 of the boys achieved Silver certificates. How many girls did not achieve Silver certificates?
Boys |
Girls |
5 u |
4 p |
Achieved Silver |
Did not achieve Silver |
Achieved Silver |
Did not achieve Silver |
3 u |
2 u |
1 p |
3 p |
Number of pupils who did not achieve Silver certificates
= 133 - 63
= 70
3 u + 1 p = 63
1 p = 63 - 3 u --- (1)
2 u + 3 p = 70
3 p = 70 - 2 u --- (2)
Make p the same.
(1)
x33 p = 189 - 9 u --- (3)
(2) = (3)
70 - 2 u = 189 - 9 u
9 u - 2 u = 189 - 70
7 u = 119
1 u = 119 ÷ 7 = 17
Number of boys who achieved Silver certificates
= 3 u
= 3 x 17
= 51
Number of girls who achieved Silver certificates
= 63 - 51
= 12
Answer(s): 12