Average expenditure of a person for the first 3 days of a week is Rs. 360 and for the next 4 days is Rs. 420. Average expenditure of the man for the whole week is:  Choices.
A) 350
B) 370
C) 390
D) 400
E) none

Rationale: "explanation : assumed mean = rs . 360 total excess than assumed mean = 4 × ( rs . 420 - rs . 350 ) = rs . 280 therefore , increase in average expenditure = rs . 280 / 7 = rs . 40 therefore , average expenditure for 7 days = rs . 360 + rs . 40 = rs . 400 correct option : d"
Answer: D