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The ratio of number of boys and girls in an art class of 720 students is 7 ∶ 5. How many more girls should join to make the ratio 1 ∶ 1?
1. 110
2. 120
3. 140
4. 150

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Correct Answer - Option 2 : 120

Given:

Total students = 720

Ratio of boys and girls in the art class = 7 ∶ 5

Required ratio = 1 ∶ 1

Calculation:

Ratio of boys and girls in the art class = 7 ∶ 5

Total students = 720

∴ Total number of boys = 720 × 7/12

⇒ 60 × 7

⇒ 420

∴ Total number of girls = 720 – 420

⇒ 300

Now, number of girls that should join to make ratio 1 ∶ 1

⇒ 420 – 300

⇒ 120

∴ 120 more girls should join to make the ratio 1  1. 

ALTERNATE METHOD:

Total number of students = 720

Boys : Girls = 7 : 5

No. of boys = 7/12 × 720

⇒ 420

No. of girls = 5/12 × 720

⇒ 300

Let no. of girls should join = x

420/(300 + x) = 1/1

⇒ 300 + x = 420

⇒ x = 120

∴ 120 more girls should join to make the ratio 1  1. 

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