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Area of a right-angled triangle

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by pareekbharat86 » Sat Nov 09, 2013 11:30 pm
In a triangle PQR, angle PQR is a right angle. QS is a line segment drawn on the hypotenuse and perpendicular to the hypotenuse. Line segment PS is 25, line segment RS is 4. What is the area of the triangle PQR?

a. 125
b.145
c. 240
d. 290
e. Cannot be determined

OA is B.

The explanation says that triangles PQS and PRS are similar to triangle PQR. How?

Source- Kaplan Practice Test 3
Last edited by pareekbharat86 on Mon Nov 11, 2013 8:33 am, edited 2 times in total.
Thanks,
Bharat.
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by theCodeToGMAT » Sun Nov 10, 2013 12:55 am
pareekbharat86 wrote:In a triangle PQR, angle PQR is a right angle. PS is a line segment drawn on the hypotenuse and perpendicular to the hypotenuse. Line segment QS is 24, line segment RS is 4. What is the area of the triangle PQR?

a. 125
b.145
c. 240
d. 290
e. Cannot be determined

OA is B.

The explanation says that triangles PQS and PRS are similar to triangle PQR. How?

Source- Kaplan Practice Test 3
Is there a typo in the question?
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by [email protected] » Sun Nov 10, 2013 12:58 am
Hi Bharat,

Have you transcribed this question correctly?

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by pareekbharat86 » Sun Nov 10, 2013 2:19 am
theCodeToGMAT wrote:
pareekbharat86 wrote:In a triangle PQR, angle PQR is a right angle. PS is a line segment drawn on the hypotenuse and perpendicular to the hypotenuse. Line segment QS is 24, line segment RS is 4. What is the area of the triangle PQR?

a. 125
b.145
c. 240
d. 290
e. Cannot be determined

OA is B.

The explanation says that triangles PQS and PRS are similar to triangle PQR. How?

Source- Kaplan Practice Test 3
Is there a typo in the question?
The error is regretted. I have edited the question.
Thanks,
Bharat.
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by theCodeToGMAT » Sun Nov 10, 2013 2:43 am
I tried ... but got bit different answer.. are you sure of the value of measurements?
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by theCodeToGMAT » Sun Nov 10, 2013 2:47 am
A Direct Shortcut
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by GMATGuruNY » Sun Nov 10, 2013 4:26 am
I believe that the problem should read as follows:
In a triangle PQR, angle PQR is a right angle. QS is a line segment drawn on the hypotenuse and perpendicular to the hypotenuse. Line segment PS is 25, line segment RS is 4. What is the area of the triangle PQR?

a. 125
b.145
c. 240
d. 290
e. Cannot be determined
Image

QS is a height drawn through the right angle of triangle PQR.

A height drawn through the right angle of a triangle forms THREE SIMILAR TRIANGLES.

In the figure above:
The angles of triangle PQS are x-y-90.
The angles of triangle QRS are x-y-90.
The angles of triangle PQR are x-y-90.
Since each triangle has the same combination of angles, the 3 triangles are similar.

Since triangle PQS is similar to triangle QRS, the ratio of the legs in each triangle must be the same.
In triangle PQS:
(side opposite x)/(side opposite y) = h/25.
In triangle QRS:
(side opposite x)/(side opposite y) = 4/h.
Since the ratios must be equal:
h/25= 4/h
h² = 4*25
h = 2*5 = 10.

Area of PQR = (1/2)bh = (1/2)(29)(10) = 145.

The correct answer is B.
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