If A = 1/5 and B = 1/8 and the average of A, B and C is 9/40. What is the value of C given that A, B and C are three rational numbers?

A 13/40

B 7/20

C 1/12

D 1/20

E None of these

Correct Answer: Option B

According to the given information,

A = 1/5

B = 1/8

Average = 9/40

We know that,

Mean = (Sum of all observations)/(Number of observations)

\(\frac{9}{{40}}{\rm{\;}} = {\rm{\;}}\frac{{\frac{1}{5} + \frac{1}{8} + {\rm{C}}}}{3}\)

\(\frac{{27}}{{40}}{\rm{\;}} = {\rm{\;}}\frac{{8 + 5}}{{40}} + {\rm{C}}\)

27/40 - 13/40 = C

C = 7/20