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Probability - Set T consists

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by fiza gupta » Sat Dec 31, 2016 9:06 am
Set T consists of all points (x,y) such that x^2 + y^2 = 1. If point (a,b) is selected from set T at random, what is the probability that b > a + 1?

A)1/4
B)1/3
C)1/2
D)3/5
E)2/3

OA:A
Fiza Gupta
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Source: — Problem Solving |

by [email protected] » Sat Dec 31, 2016 10:16 am
Hi fiza gupta,

This question is fairly 'high-concept', but you can solve it with a drawing and a bit of logic.

When you graph the equation X^2 + Y^2 = 1, you will have a circle with a radius of 1 that is centered around the Origin. There are only four points on that circle that are integer values: (0,1), (1, 0), (0, -1) and (-1, 0). All of the other points are positive/negative fractional values. Knowing that, the ONLY way for the inequality Y > X + 1 to occur is when X is NEGATIVE and Y is POSITIVE. That outcome only occurs in the 2nd quadrant of the graph (which is 1/4 of the circle). While you might be unsure about whether every point in that quadrant would 'fit' the inequality or not, the answer choices ARE numbers - and the smallest of them is 1/4. Since there's no smaller possibility, 1/4 must be the answer.

Final Answer: A

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by GMATGuruNY » Sat Dec 31, 2016 3:07 pm
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by fiza gupta » Sun Jan 01, 2017 6:55 am
Thanku Experts! :)
Fiza Gupta
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