Problem Solving

My answer is 78 however, I need help in trying to solve this one. I'm clueless.
Webb

What would be the solution if the question stated the co ordinates to be 1<x<=3 and 1<y<=3

satts wrote:What would be the solution if the question stated the co ordinates to be 1<x<=3 and 1<y<=3

I think 4. Assuming integral values.

nice approach indeed.Good learning for me.

Brent@GMATPrepNow wrote:

awesomeusername wrote:A bit tricky.

There are 9 points in the restricted plane. There are three points to a triangle.

9C3 = 9!/3!*6! = 7*8*9/6 = 84

There are four 3 point sets that don't create triangles (when x is the same for all points, or y is the same for all points).

So 84-4 = 80

The first part of your solution looks good (9C3), but we need to subtract more than 4 3-point sets.

Here's my full solution:

thanks for the answer

Hello,

I am completely starting new so still learning about all of this. Is it 9C3 because 3 points to 3 sides of triangle. And then is it multiplied by 6! because its 9-3?

Thanks.

nice conceptual question.

got it today in daily quant. mail.

what is the final answer guys. its very confusing if all give theis own answers..

ans: 76

9C2 - ( 3 horizontal point sets + 3 vertical point sets + 2 cross point sets) = 76

whether GUESS or NOT
I am Selecting ANSWER:A

iMO 76 ...
total 9 points
total combination 9C3 = 84


exclude 8 lines ( they will not form triangle- as they are straight lines)
A B C




D E F




G H I

exclude the below lines
1) G-H-I
2) A-B-C
3) D-E-F
4) A-D-G
5) B-E-H
6) C-F-I
7)G-E-C
8)A-E-I


so ans = 84-8 = 76

9C3-8 = 76

9c3 selections out of 9 points.
3 vertical , 3 horizontal and 2 diagonal selection lie on straight lines. Hence we have to subtract 8 from the result.

This is a good one. The answer is indeeed 76.
A very simple explanation goes like this

There are total 9 valid points > 9C3
out of then 6 lie on horizontal and vertical planes, 2 lie on the diagonals
therefore 9C3 - 8 = 84-8 = 76

rajs2010 wrote:

rajs2010 wrote:

[email protected] wrote:I do not understand the logic behind these Daily GMAT Questions. The questions are only being answered by other students and never given a confirmed correct answer. If this is really the case, continuing in these discussions would be like the Blind Leading the Blind. Will the instructor giving these questions out ever give the correct answer?

I agree..I subscribed to the daily questions yesterday and got the very first email today....It'll be really helpful if the correct answer is published too, with these daily questions...

If the idea is to promote some healthy discussion first on these questions to explore all the possible ways one could go wrong,it might be a good idea to have the correct answer by the Moderator/Expert in next days email...

If you guys would just look at the user/instructor that posted the question (Brent@GMATPrepNow) & scroll donw, you would see that after some good discussion & critical thinking, he answered the question. Same with all other Daily questions. It helps to see how others got the same answer differently AND it helps see other people's mistakes to learn from them I hate the GMAT, but having a team of problem solvers helps open my mind to other solving possibilities.