The average of 48 numbers is 78. If we subtract a number "X" from each number, then the average becomes 57. What is the value of X?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 21.
We know that,
Average = Sum of observations/Number of observations
Sum of 48 numbers = 48 × 78 = 3744
If we subtract "X" from each number = 3744 - X
⇒ (3744 - 48X)/48 = 57
⇒ 3744 - 48X = 2736
⇒ 3744 - 2736 = 48X
⇒ 48X = 1008
⇒ X = 1008/48
⇒ X = 21
Hence, the value of X is 21