If variance of x is 24, then what is the variance of (x+1)/2?

A)24

B)12.5

C)24.5

D)6

E)8

It seems tough since you don't have the data. If you have the data, you could add 1 to each of them then divide by 2. Now you don't have them

(24+1)/2=12.5 ? WRONG

Rules:

1-Variance of X if added or subtracted by a number, remains the same

2- Variance of X if multiplied or divided by a number, is multiplied or divided by that number squared.

So, let's write (x+1)/2 in this way:

x/2 + 1/2

considering rule #1, we omit the second part, 1/2.

So, now we wanna calculate the variance for x/2.

As rule #2 say, we should divide 24 by 4 (2 squared)

solution= 6Source: my own question. I know it's not a standard GMAT question, but who knows, maybe GMAC decides to continue ever growing difficulty of GMAT by including these easy rules

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