155 pupils went for a spelling test and 72 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
= 155 - 72
= 83
3 u + 1 p = 72
1 p = 72 - 3 u --- (1)
2 u + 3 p = 83
3 p = 83 - 2 u --- (2)
Make p the same.
(1)
x33 p = 216 - 9 u --- (3)
(2) = (3)
83 - 2 u = 216 - 9 u
9 u - 2 u = 216 - 83
7 u = 133
1 u = 133 ÷ 7 = 19
Number of boys who achieved Silver certificates
= 3 u
= 3 x 19
= 57
Number of girls who achieved Silver certificates
= 72 - 57
= 15
Answer(s): 15
