If a certain toy store's revenue in November was 2/5 of its revenue in December and its revenue in January was 1/3 of its revenue in November, then the store's revenue in December was how many times the average (arithmetic mean) of its revenues in November and January? Choose the correct choice from the following choices.
A) 5 / 3
B) 5 / 4
C) 10 / 3
D) 15 / 4
E) 15 / 2

Rationale: "n = 2 d / 5 j = n / 3 = 2 d / 15 the average of november and january is ( n + j ) / 2 = 8 d / 15 / 2 = 4 d / 15 d is 15 / 4 times the average of november and january . the answer is d ."
Answer: D