It's just a slightly different way of making the calculation. The way you calculated, you just multiplied by 2 to get the sum for each of the three statements before you added them. The OA adds them before it multiplies out the 2.

Adding the statements:
x + y = 20
y + z = 36
x + z = 40
--------------------
2(x + y + z) = 96
(x + y + z) = 48
(x + y + z)/3 = 16

Taking the average of the averages, you leave the /2 in each term:
[(x + y)/2 + (y + z)/2 + (x + z)/2] / 3 = (20/2 + 36/2 + 40/2) / 3
[2(x + y + z) / 2] / 3 = 48/3
(x + y + z)/3 = 16

Both methods just happen to bring you to the answer.

Thanks man. I know by calculation that both are same. I want to know the concept behind taking the avg of the averages here.

bump

Hi,
There is no underlying concept in this. It is just the same thing interpreted in two ways. So, no need to worry about any concept here.

I just learned from Kaplan that you can take the average of the averages when the sets have equal no. of terms. Like in two sets of 60 items combined. Avg of new Set = Avg Set A +Avg Set B/ 2

If the no. of terms aren't equal in both sets, then it's weighted average.

now can someone tell me how this apply to this example?

The average of x and y is 10. The average of y and z is 18. And the average of x and z is 20. What is the average of x, y and z?

2(x+y+z) = 20+36+40 = 96
x+y+z = 48

thus (x+y+z)/3 = 48/3=16