The average of a, b and c is 20 and that of b, c and d is 25. If d = 30, then the value of a is :
25
45
30
15
Correct Option: D
According to the question, a + b + c = 3 × 20 = 60 ...(i) b + c + d = 3 × 25 = 75 ...(ii) By equation (i) – (ii), a – d = 60 – 75 ⇒ a – 30 = – 15 ⇒ a = 30 – 15 = 15
