during the last 4 years , a large truck company purchased diesel at rates of $ 1.2 , $ 1.3 , $ 1.8 and $ 2.1 per gallon . what was the mean cost of diesel over the 4 - year period if the company spends the same amount of dollars on diesel each year ? Choose the correct choice from the following answers:
A) $ 2.5
B) $ 2.55
C) $ 1.52
D) $ 3.25
E) $ 3.0

Rationale: finding the harmonic mean here . hm = 4 / ( 1 / 12 + 1 / 13 + 1 / 18 + 1 / 21 ) = 15.18 c
Answer: C