Answer:
a) 1/5 are Primary 6 girls
b) 120 Computer Club pupils
Explanation:
For problems like this, we assume the designated groups are one of two groups: (boys, girls), (Primary 6, Not Primary 6). That means the fractions in each group total 1.
3/4 are boys means 1-3/4 = 1/4 are girls.
a)
If 4/5 of the girls are Primary 6, then (4/5)(1/4) = 1/5 of all club pupils are Primary 6 girls
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b)
1-4/5 = 1/5 of the girls in the club are not Primary 6 girls. 1/4 of the club members are girls, so the fraction of club members who are not Primary 6 girls is ...
(1/5)(1/4) = 1/20 . . . . club pupils who are girls not from Primary 6
This fraction is 6 girls, so the total number of club pupils is ...
20×6 = 120 . . . pupils in the computer club