probability (plane)

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 131
Joined: Tue Aug 05, 2008 3:28 pm
Thanked: 2 times

probability (plane)

by mariah » Fri Jan 23, 2009 1:37 pm
36.A square with points (1,1),(-1,1),(-1,-1)&(1,-1). What is the probability that point P(x,y) is within the square? where x^2+y^2=1.

please explain !
Source: — Problem Solving |

User avatar
Site Admin
Posts: 2567
Joined: Thu Jan 01, 2009 10:05 am
Thanked: 712 times
Followed by:550 members
GMAT Score:770

by DanaJ » Fri Jan 23, 2009 1:45 pm
I would say that the probability is 1, meaning that all points P(x,y) with x^2+ y^2 = 1. What is the OA?

This is easily explained by the formula. x^2 + y^2 =1 is actually the equation of a circle with O(0,0) (center of circle) and radius 1. A radius of 1 means that the circle will "touch" our square in four points: (1,0), (-1,0), (0,1), (0,-1) and be inscribed in the circle.

The general formula for a circle is (x - a)^2 + (y - b)^2 = r^2, with r = radius and O(a,b) the center of the circle.

Master | Next Rank: 500 Posts
Posts: 160
Joined: Sat Dec 20, 2008 9:12 pm
Thanked: 11 times

by aroon7 » Fri Jan 23, 2009 5:16 pm
it will be area of circle/Area of the square
radius of circle is 1 and side of the square is 2
so answer is pi/4

what is the OA?
--------------------------
i am back!

User avatar
Master | Next Rank: 500 Posts
Posts: 226
Joined: Tue Jan 13, 2009 1:27 pm
Thanked: 23 times
Followed by:1 members

by awesomeusername » Fri Jan 23, 2009 7:50 pm
I'm going to have to agree with Dana here. If the circle in inscribed in the square, then that would mean that all points fall within the bounds of the square, so the probability would have to be 1, right?

User avatar
Site Admin
Posts: 2567
Joined: Thu Jan 01, 2009 10:05 am
Thanked: 712 times
Followed by:550 members
GMAT Score:770

by DanaJ » Fri Jan 23, 2009 10:44 pm
The formula that aroon7 provided actually represents the probability of a point in the square to be in the circle also. The question is about points in the circle that fall in to the square, IMHO....

Master | Next Rank: 500 Posts
Posts: 160
Joined: Sat Dec 20, 2008 9:12 pm
Thanked: 11 times

by aroon7 » Sat Jan 24, 2009 7:21 am
DanaJ wrote:The formula that aroon7 provided actually represents the probability of a point in the square to be in the circle also. The question is about points in the circle that fall in to the square, IMHO....
you are right danaj...
i misunderstood the question.
--------------------------
i am back!

Master | Next Rank: 500 Posts
Posts: 131
Joined: Tue Aug 05, 2008 3:28 pm
Thanked: 2 times

by mariah » Thu Jan 29, 2009 2:33 pm
oa pai/4
I have collected it from internet so oa may be inaccurate,

Master | Next Rank: 500 Posts
Posts: 221
Joined: Wed Jan 21, 2009 10:33 am
Thanked: 12 times
Followed by:1 members

by krisraam » Thu Jan 29, 2009 8:32 pm
Answer is 1