Question : The average of 21 numbers is 60. If each number is increased by 20, then find the number by which the average is increased.
Option 1: 12
Option 2: 18
Option 3: 15
Option 4: 20
Correct Answer: 20
Solution :
The average of 21 numbers = 60
Sum of the numbers = 21 × 60 = 1260
When each number is increased by 20, the new average becomes 80.
Sum of the numbers = 21 × 80 = 1680
Difference = 1680 – 1260 = 420
Average of the difference = $\frac{\text{Difference}}{\text{Total numbers}}=\frac{420}{21}=20$
Hence, the correct answer is 20.
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