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.