Advanced Mathematics Primary 6 Ratio

In a group of 30 students, 2/5 of them are boys. After 3 girls leave the group, what is the new ratio of boys to girls?

A 4 : 5
B 2 : 3
C 2 : 5
D 4 : 7
Show Worked Solution

Worked Solution

Step 1: Find the number of boys. 2/5 of 30 = 2/5 × 30 = 12 boys Step 2: Find the original number of girls. 30 − 12 = 18 girls Step 3: Apply the change — 3 girls leave. New number of girls = 18 − 3 = 15 Step 4: Write and simplify the new ratio. Boys : Girls = 12 : 15 Divide both by HCF 3: 12 ÷ 3 : 15 ÷ 3 = 4 : 5 The new ratio of boys to girls is 4 : 5.

Correct answer: 4 : 5

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