The last digit of which one of the following results equals the last

In trying to find out the units digit, the question also asks us to find out the average of \(3^2\) and \(5^2\).

Average of \(3^2\) and \(5^2\) = \(\frac{9 + 25}{2}\) = 17.

So, the units digit of the average of \(3^2\) and \(5^2\) = 7.

In option A, sum of 13 and 25 = 38. Units digit of 38 is not the same as the average of the \(3^2\) and \(5^2\). Option A can be eliminated.

In option B, sum of 3 and \(5^2\) = 3 + 25 = 28. Here also, units digit of 28 is not the same as the average of \(3^2\) and \(5^2\). Option B can be eliminated.

In option C, average of 13 and 25 = \(\frac{13 + 25}{2}\) = \(\frac{38}{2}\) = 19. Units digit is 9 and not 7. Option C can be eliminated.

In option D, average of 13 and 15 = \(\frac{13 + 15}{2}\) = \(\frac{28}{2}\) = 14. Units digit is 4 and not 7. Option D can be eliminated.

Option E has to be the answer, so let’s evaluate. Average of 19 and 35 = \(\frac{19 + 35}{2}\) = \(\frac{54}{2}\) = 27.

Units digit of 27 is the same as the units digit of the average of \(3^2\) and \(5^2\).
The correct answer option is E.

In questions like these, where there’s absolutely nothing to challenge you conceptually, just ensure that you do not make silly mistakes in interpretation of the question or the options. Because, on the GMAT, when you come across such simple questions, you just cannot afford to answer them wrongly; doing this will never let your reach those higher levels.

Hope this helps!