Correct Answer - Option 2 : 30
Given:
Average of seven numbers = 24
Average of first six numbers = 21
Last number is replaced by its twice.
Calculations:
Let the sum of seven numbers and first six numbers be x and y respectively.
Average = x/7
⇒ x/7 = 24
⇒ x = 168
Let, sum of first six numbers be y.
⇒ y/6 = 21
⇒ y = 126
Last number = 168 – 126 = 42
Twice of last number = 42 × 2 = 84
The sum of 7 numbers become,
⇒ 126 + 84 = 210
New average of 7 numbers = 210/7 = 30
∴ New average is 30.