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Test some small numbers: \frac{2^2+4^2}{2}=10=3^2+1 or: \frac{4^2+6^2}{2}=26=5^2+1.

APPROACH #2:

Say 54,821=x, then \frac{54,820^2+54,822^2}{2}=\frac{(x-1)^2+(x+1)^2}{2}=x^2+1=54,821^2+1.

APPROACH #3:

The units digit of 54,820^2+54,822^2 is 0+2=4. Now, since 54,820^2+54,822^2 must be a multiple of 4, then \frac{54,820^2+54,822^2}{2} must have the units digit of 2. Only answer choice D fits.

Re: The mean of (54,820)^2 and (54,822)^2 = [#permalink]
10 Dec 2012, 02:04

Shrink the monster technique. The two numbers are two consecutive even numbers raised to 2. Shrink the monster and think of baby numbers such as 0 and 2.

mean=\frac{{0^2 + 2^2}}{2}=2

Substitute you baby numbers to the answer choices.

Re: The mean of (54,820)^2 and (54,822)^2 = [#permalink]
10 Dec 2012, 03:42

2

This post received KUDOS

Ans: Replace 54820 by x and 54822 by (x+2) and then solve by algebra. Mean of x^2 and (x+2)^2 is x^2+2x+2 which can be written as x^2+2x+1+1. So the answer is (D)
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