If the average cost of 5 commodities is 20 units and the average cost of 3 of those commodities is 15 units, then find the average cost of the remaining two commodities.?

Your question was – If the average cost of 5 commodities is 20 units and the average cost of 3 of those commodities is 15 units, then find the average cost of the remaining two commodities? A few days ago I take part an exam where I have faced this GMAT questions and my answers option were – a. 20.5 b. 21.5 c. 22.5 d. 26.5 e. 27.5 I have answered as my Correct answer is = E Because of this following Explanation: According to  the question, The average cost of 5 commodities = 20 units......i The average cost of 3 of those commodities = 15 units......ii We have to find the average cost of the remaining 2 of those commodities. Let the commodities be a, b, c, d, e Hence, from i we can say that, a+b+c+d+e/5 = 20 ∴ a+b+c+d+e = 20*5 = 100 ......iii Also, from ii we can say that, a+b+c/3 = 15 ∴ a+b+c = 15*3= 45 .....iv Now, substituting equation iv in equation iii, we get, 45+d+e = 100 ∴ d+e = 100 - 45 ∴ d+e = 55 But, we have to find their average. Hence, dividing both sides by 2 we get, d+e/2 =55/2 = 27.5 Hence, the correct answer is option e. Hope you have got your answer. Thanks.