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A ladder of a fire truck is elevated to an angle of 60° and

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A ladder of a fire truck is elevated to an angle of 60° and [#permalink] New post 07 Jun 2012, 01:16
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A ladder of a fire truck is elevated to an angle of 60° and extended to a length of 70 feet. If the base of the ladder is 7 feet above the ground, how many feet above the ground does the ladder reach?

(A) 35
(B) 42
(C) 35\sqrt{3}
(D) 7 + 35\sqrt{3}
(E) 7 + 42\sqrt{3}
[Reveal] Spoiler: OA

Last edited by Bunuel on 07 Dec 2012, 05:04, edited 1 time in total.
Edited the question.
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Re: maths problem [#permalink] New post 07 Jun 2012, 01:47
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Vertical height of ladder = 70.sin(60) = 35root3

Total height = 7 + 35root3
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Re: A ladder of a fire truck is elevated to an angle of 60° and [#permalink] New post 07 Jun 2012, 11:50
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Notice that trigonometry is not tested on the GMAT, which means that EVERY GMAT geometry question can be solved without it.

sarb wrote:
A ladder of a fire truck is elevated to an angle of 60° and extended to a length of 70 feet. If the base of the ladder is 7 feet above the ground, how many meet above the ground does the ladder reach?

A. 35
B. 42
C. 35 root 3
D. 7 + 35 root 3
E. 7 + 42 root 3


Look at the diagram below:
Attachment:
Ladder.png
Ladder.png [ 5.44 KiB | Viewed 6051 times ]
Triangle ABC is a 30°-60°-90° triangle. Now, in a right triangle where the angles are 30°, 60°, and 90° the sides are always in the ratio 1 : \sqrt{3}: 2, the leg opposite 30° (AC) corresponds with 1, the leg opposite 60° (BC) corresponds with \sqrt{3} and the hypotenuse AC corresponds with 2. So, \frac{BC}{AB}=\frac{\sqrt{3}}{2} --> \frac{BC}{70}=\frac{\sqrt{3}}{2} --> BC=35\sqrt{3}.

Hence the leader reaches 7+35\sqrt{3} above the ground.

Answer: D.

For more check Triangles chapter of Math Book: math-triangles-87197.html

Hope it helps.
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Re: A ladder of a fire truck is elevated to an angle of 60° and [#permalink] New post 07 Jun 2012, 19:21
Bunuel wrote:
Notice that trigonometry is not tested on the GMAT, which means that EVERY GMAT geometry question can be solved without it.

sarb wrote:
A ladder of a fire truck is elevated to an angle of 60° and extended to a length of 70 feet. If the base of the ladder is 7 feet above the ground, how many meet above the ground does the ladder reach?

A. 35
B. 42
C. 35 root 3
D. 7 + 35 root 3
E. 7 + 42 root 3


Look at the diagram below:
Attachment:
Ladder.png
Triangle ABC is a 30°-60°-90° triangle. Now, in a right triangle where the angles are 30°, 60°, and 90° the sides are always in the ratio 1 : \sqrt{3}: 2, the leg opposite 30° (AC) corresponds with 1, the leg opposite 60° (BC) corresponds with \sqrt{3} and the hypotenuse AC corresponds with 2. So, \frac{BC}{AB}=\frac{\sqrt{3}}{2} --> \frac{BC}{70}=\frac{\sqrt{3}}{2} --> BC=35\sqrt{3}.

Hence the leader reaches 7+35\sqrt{3} above the ground.

Answer: D.

For more check Triangles chapter of Math Book: math-triangles-87197.html

Hope it helps.


Thank you that made it very simple :)
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Re: A ladder of a fire truck is elevated to an angle of 60° and [#permalink] New post 21 Feb 2013, 10:31
which one of 2 angles is 60?

the question is not clear.
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Re: A ladder of a fire truck is elevated to an angle of 60° and [#permalink] New post 21 Feb 2013, 10:38
Since the questions says elevated at an angle of 60 deg, the base angle is 60 deg. By default, elevation is from baseline and since the ladder is placed parallel to x axis, the elevation is also from x axis.

Hope that helps!

thangvietnam wrote:
which one of 2 angles is 60?

the question is not clear.

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Re: A ladder of a fire truck is elevated to an angle of 60° and   [#permalink] 21 Feb 2013, 10:38
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