Correct Answer - Option 2 : 12

**Given:**

In a class average weight of students was 51 kg.

After some days 2 students joined the class

The average was increased by 1.2 kg.

Total weight became 626.4 kg.

**Formula used:**

Average = Sum of observations/Number of observations

**Calculation:**

Let number of students before joining 2 students be x

Total weight of x students = 51x kg

After joining of 2 students, total number of students = x + 2

Average weight now = (51 + 1.2) kg

⇒ 52.2

Total weight of (x + 2) students = 52.2(x + 2) kg

52.2(x + 2) = 626.4

⇒ 52.2x + 104.4 = 626.4

⇒ 52.2x = 522

⇒ x = 10

So, total number of students after joining of 2 students = 10 + 2 = 12

**∴ The required number of students is 12**