LevanKhukhunashvili wrote:

Took too much time, 3:20

Am I supposed to waste more than 3 minutes on such time consuming examples?

It's a 45 second question at max if you find the pattern and apply it. FWIW, took me 58 seconds with the check to confirm accurate answer (more on that below). That's where the trick lies in all GMAT problems.

**Quote:**

30(799) + 15(799) +15(799) + 20(799) + 15(799) + 4(799) + 798 is equal

Here is how I did it:

a(y) + b(y) + c(y) + d(y) is the same as (a+b+c+d)*y. In the case above: (30 + 15 + 15 + 20 + 15 + 4) * 799. Now you can either solve for 799 * 99 (the sum from before) and then add the 798 or you can do the following:

(30 + 15 + 15 + 20 + 15 + 4) * 799 + 799 - 1 --> 799*(99 + 1) - 1 --> 799 * 100 - 1 --> 79,900 - 1 --> 79,899. If you trust yourself, you could even get away without writing anything down on paper for this sort of issue, but why take that risk?

How do you check the answer?

1. Confirm the sum (30 + 15 + 15 + 20 + 15 + 4) is correct

2. Since the sum is 99 and you're multiplying by 99+1 and the subtracting 1, you know the last digit will be a 9. Reject A.

3. You're left with 4 options now. No check here. All end in 9. Just confirm the math quickly.

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