Option 3 : 47 years

Age of the man who left the group

⇒ Initial average + New total of numbers × change in average

Initial average = 36, Change in average = 1, New total number = 11

⇒ 36 + 11 × 1

⇒ 47

**∴ The age of the man who left the group is 47 years.**

**Given:**

Average = 36 years

Total members = 12

Decreased in average = 1

**Formula used:**

Average = The sum of all members/Total members

**Calculation:**

Average = The sum of all members/Total members

⇒ 36 = The sum of all members/(12)

⇒ The sum of all members = 432 ---(1)

According to the question,

New average = 36 - 1

⇒ New average = 35 years

Total members = 11

⇒ The sum of remaining members = New average × Total members

⇒ The sum of remaining members = 35 × 11

⇒ The sum of remaining members = 385 ---(2)

The age of the man who left the group,

⇒ 432 - 385

⇒ 47 years

∴ The age of the man who left the group is 47 years.