The average of 7 numbers is 51. If each number is increased by 7, what will the new average be?

Correct option is D

Given:
Number of values = 7
Original average = 51
Increase in each number = 7
Formula Used: 
Average$$=\frac{\text{(Sum of numbers)}}{\text{(Total number)}}$$​​
Solution:
The sum of the original 7 numbers = Average $$\times$$​ Number of values = 51$$\times$$ 7 = 357.​
If each number is increased by 7, the total increase in the sum will be 7$$\times$$7 = 49.​
The new sum will be 357 + 49 = 406.
The new average = $$\frac{\text{New Sum}}{ \text{Number of values}} = \frac{406}{7} = 58$$​​
Alternate Method:
Since each number is increased by 7, the average will also increase by 7.
Therefore, the new average = Original average + Increase = 51 + 7 = 58.

Thus, option (d) is right.