Point P(a,b) is randomly selected in the region enclosed by the follow

Question

Point P(a, b) is randomly selected in the region enclosed by the following lines: 3y + 2x = 6, x = 0 and y = 0. What is the probability that b > a ?

A. 1/10
B. 1/5
C. 2/5
D. 3/5
E. 4/5

Bunuel · Accepted Answer

Refer to the diagram below: Probability.png The area of the triangle enclosed by 3y + 2x = 6 (y=2-2/3*x), x=0 and y = 0 is 1/2*2*3=3. We need the y-coordinate of P to be greater than its x-coordinate (y>x), so point P must be above line y=x and in the enclosed region. The probability of that is (favorable)/(total)=(yellow triangle)/(entire triangle). Now, we need to find intersection point of y=x and 3y+2x=6, which is (6/5, 6/5). Thus the area of yellow triangle is 1/2*6/5*2=6/5. P=(6/5)/3=2/5. Similar questions to practice: set-t-consists-of-all-points-x-y-such-that-x-2-y-2-1-if-15626.html in-the-coordinate-plane-rectangular-region-r-has-vertices-a-104869.html in-the-xy-plane-a-triangle-has-vertexes-0-0-4-0-and-86926.html in-the-xy-plane-a-triangle-has-vertexes-0-0-4-0-and-88395.html Hope it helps.

Bunuel · Answer

Look at the diagram below: Untitled.png The base of the triangle is 2 (vertical green line) and the height of the triangle is 6/5 (horizontal green line, x-coordinate of the intersection point). So, the area is /2*6/5*2=6/5. Check other Probability and Geometry questions in our Special Questions Directory .

ronr34 · Answer

Hi Bunuel,
Can you explain how you calculated the area of the triangle?

GovindAgrawal · Answer

how do we get this point of intersection?

Shruti0805 · Answer

Hi,

Let me try explaining. It took me a while figuring it out myself.

First, we can replace the lines x=0 and y=0 by a line x=y. That leaves us with just 2 lines :- 1st is x=y and 2nd is 3y= -2x + 6.

To find the intersection of these 2 lines, equate the RHS variables and you'll get x=6/5.    
Now, substitute the value of x in either of the 2 equations and you'll get the y coordinate for the point.

Does that help ?

GMATinsight · Answer

Just a little clarification.

We do NOT have to replace lines x=0 and y=0 with x=y

Instead we need to understand that y and x co ordinate are equL on line y=x I.e. on that line a=B

But since we need b>a so we need all points above line y=x which are bounded by other three lines which are
x=0
y=0
And -2x+6 = 3x

I hope this helps

Noida · Answer

Can someone explain why probability is being calculated using area?

Also, if the question asked for only integer values, how will the answer change? Will it be 1/5?

bumpbot · Answer

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Point P(a,b) is randomly selected in the region enclosed by the follow

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Point P(a,b) is randomly selected in the region enclosed by the follow

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