John found that the average of 15 numbers is 40. If 10 is added to each number then the mean of number is?  Choose the correct choice:
A) 50
B) 60
C) 75
D) 80
E) 85

Rationale: "( x + x 1 + . . . x 14 ) / 15 = 40 50 option a"
Answer: A