Question

Average age of class of 72 students is 20 years. Two girls of age 20 and 22 years leave the class and a new boy joins. If new average age is same as previous one then find age of new boy.
1. 22
2. 20
3. 18
4. 14

Answer 1

Correct Answer - Option 1 : 22

Given:

72 students = 20 years (Average age)

Two girls removed – 20 and 22 age

New average = 20 years

Formula used:

Average of X = (X1 + X2 + X3 + X4….. + Xn)/ n

Calculation:

Average of 72 = 20

⇒ Total age of 72 students = 72 × 20

⇒ Total age of 72 students = 1440

⇒ Two girls removed = 1440 – (20 + 22)

⇒ Two girls removed = 1398

Now, let age of new boy be X

⇒ Total number of students = 70 + 1 (New boy added)

⇒ Total age of 71 students = 71 × 20

⇒ Total age of 71 students = 1420

⇒ Total age of 71 students = 1398 + X

⇒ 1398 + X = 1420

⇒ X = 22

∴ Age of new boy is 22