On one of the gmat problems I was making a factor tree and I stopped factoring because I thought 143 (11 x 13) was prime. I checked if it was divisible by 1-10, since it wasn't I concluded it was prime. Anyone have any tips to avoid this mistake?
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Stumped by the number 143
Source: Beat The GMAT — Problem Solving |
I think you should have checked till 12 and not just 1-10. Because, 143 is a number closer to 144 (which is a square of 12). So, you need to check till 12. Had you checked till 12, you would have found that 11 divides 143 and the quotient gets you 13.
