Quant Flashcard Group 1 - Sum of Integers in Interval

GRE Quant Problem Solving
1

In the Sum of Integers in Interval section of the Quant Flashcard Group 1, there is a method called Ingenuity. My question is how to determine the number of integers in an evenly spaced set according to the Ingenuity method?

1600×900 191 KB

2

Get the number of integers in the set n = L - A + 1. In case of the space between each consecutive integer being greater than 1 (Eg. all multiples of 3 between 50 and 300), L and A will be the first and last multiples of the space between consecutive integers (3 in the example) respectively, and the formula becomes ([L + A)/space] + 1.

Get the median, which is:
the middle value if n is odd
average of two middle values if n is even.

Now multiply the median into n.

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3

Thanks for your clues.

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