### RE: 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.?

I cannot solve this problem – Can anyone help me?

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.

Thanks

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.