Yesterday, Integrated Learning posted a 700 level GMAT question on our blog. Today, they have followed up with the answer:
Whenever you need to find the sum of consecutive numbers, you must follow three steps: 1. Find the middle 2. Find the number of numbers 3. Multiply
For 1 – 40, the middle is found by averaing the end points: 41/2 = 20.5.
Since the first number is 1, it should be obvious that the number of numbers is 40.
So the sum of this series is 20.5 x 40 = 820.
Now the greatest prime factor is easy. Just break down 820: 2 x 2 x 5 x 41
The answer is C.
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