mikemcgarry wrote:
jakeqs wrote:
Not sure if this works but seems the easiest way would be to find area of the circle=36Pi and subtract the 4 lattice points on the circle. Maybe it only works in this example and not always.
Dear
jakeqs,
As I expressed to
tvrs09 above, what you are suggesting is an approximation method. Estimation is a perfectly fine strategy for the GMAT Quant.
If the answers are spread out, then estimation has a better chance of determining a unique answer. In what you suggested here, it was a totally lucky fluke that it wound up with the exact answer. Often, estimation does not produce an exact answer, but that's OK. Again, if the answer choices are widely space apart, then estimation is often enough to determine a single answer.
Does all this make sense?
Mike
Mike,
This is a beautiful question. I approached this sort of like a permutations problem. We have x^2 + y^2 < 36 for points to lie inside the circle.
Taking integer squares we can consider 0,1,2,3,4,5,-1,-2,-3,-4,-5. 11 in total.
For 0,1,2,3,-1,-2,-3: we can have 11 possible pairs (including itself): 11*7 = 77
For 4,-4: we can't have 5 or -5: 2 * (11-2) = 18
For 5,-5: we can't have 5,-5,4,-4: 2 * (11-4) = 14
77 + 18 + 14 = 109.
Hope this is also an alternate simple method.