Sum of multiples in interval question for Greg

In the prep swift video you have the example problem:

“Find multiples of 5 in the interval 105-355 (inclusive)”
-We determine that each pair adds up to 460 ✓
-We determine that there are an odd number of multiples (51: 25 pairs + 1 extra in the middle) ✓
-But then you say to solve we need to determine what that middle number is and add it in to (460x25). But isn’t it simpler if we just do 460 x 25.5? Is there a reason to not do this? It seems that the answer is the same.

Thank you!

The answer will be the same in either method. I think it is a personal choice to choose which method to use. Even, if you see below quant flashcard, you notice that the Greg showed two methods to solve this type of question.

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