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# In the figure above, line AC represents a seesaw that is

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Manager
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In the figure above, line AC represents a seesaw that is [#permalink]  03 Oct 2006, 04:34
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Untitled.png [ 1.22 KiB | Viewed 2806 times ]
In the figure above, line AC represents a seesaw that is touching level ground at point A. If B is the midpoint of AC, how far above the ground is point C?

(1) x = 30
(2) Point B is 5 feet above the ground.
[Reveal] Spoiler: OA

Attachments

fig1.doc [20.5 KiB]

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ARISE AWAKE AND REST NOT UNTIL THE GOAL IS ACHIEVED

Last edited by Bunuel on 29 Nov 2013, 01:25, edited 1 time in total.
Edited the question and added the OA.
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20. In the figure above, line AC represents a seesaw that is touching level ground at point A. If B is the midpoint of AC, how far above the ground is point C?
(1) x = 30
(2) Point B is 5 feet above the ground.

A & B are unsufficient.

Combining

Sin 30(degree) = 5/AB
so AB can be determine and hence AC, since AC=2AB.

If we draw a perpendicula from line A which touches point C and call that point (on line A) D.

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Statement 2 alone is suff.
lets say: BA= x
then CA = 2x (since B is the mid point of CA)
Triangle ACD(D is the point where the perpendicular dropped from C touches the ground) is similar to triangle ABE(E is the point where the perpendicular dropped from C touches the ground).
Therefore x/5=2x/z
or z=10
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This one had me stumped. But, B it is, as others have explained before.
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It is B.
Apply property of similar triangles.........
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Last edited by cicerone on 25 Sep 2008, 00:30, edited 1 time in total.
Manager
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Kudos [?]: 14 [0], given: 18

Gud explanation 800_gal...

Thanks for that..hahaa..completely forgot about the similar triangles properties...gotto revise it now...
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ARISE AWAKE AND REST NOT UNTIL THE GOAL IS ACHIEVED

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Re: In the figure above, line AC represents a seesaw that is [#permalink]  28 Nov 2013, 13:57
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Raghavender wrote:
20. In the figure above, line AC represents a seesaw that is touching level ground at point A. If B is the midpoint of AC, how far above the ground is point C?
(1) x = 30
(2) Point B is 5 feet above the ground.

Is there anyway someone can put the picture on the problem so we don't have to open it every time?

Much appreciated!
Cheers
J
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Re: In the figure above, line AC represents a seesaw that is [#permalink]  29 Nov 2013, 01:25
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Expert's post
jlgdr wrote:
Raghavender wrote:
20. In the figure above, line AC represents a seesaw that is touching level ground at point A. If B is the midpoint of AC, how far above the ground is point C?
(1) x = 30
(2) Point B is 5 feet above the ground.

Is there anyway someone can put the picture on the problem so we don't have to open it every time?

Much appreciated!
Cheers
J

______________
Done.
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Re: In the figure above, line AC represents a seesaw that is [#permalink]  05 May 2015, 08:10
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Re: In the figure above, line AC represents a seesaw that is [#permalink]  06 May 2015, 02:02
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Hi All,

For those of you who are not comfortable with the concept of similar triangles and its application, this question can be solved using application of simple trigonometric ratios.

In triangle ABD which is right angled at D, we can use $$Sin x = \frac{BD}{AB.}$$

Similarly, in triangle ACE which is right angled at E, we can use $$Sin x = \frac{CE}{AC}$$

From the above two equations, we can write $$\frac{BD}{AB} = \frac{CE}{AC}$$ i.e. $$CE = \frac{(BD * AC)}{AB.}$$

Since $$AC = 2AB$$, we can write $$CE = 2BD$$.

So, for finding the height of point C from the ground we just need to know the height of point B from the ground.

We see that st-II provides us the height of B. Thus statement-II alone is sufficient to answer the question.

You can try out a similar question at a-squirrel-climbs-a-straight-wire-from-point-a-to-point-c-if-b-is-the-195315.html#p1517662

Hope its clear!

Regards
Harsh
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In the figure above, line AC represents a seesaw that is [#permalink]  25 Jul 2015, 04:40
What i don't get is why we can assume that the two triangles are similar just because AB = BC?

I mean it looks similar, but why can we apply that?
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In the figure above, line AC represents a seesaw that is [#permalink]  25 Jul 2015, 05:01
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noTh1ng wrote:
What i don't get is why we can assume that the two triangles are similar just because AB = BC?

I mean i looks similar, but why can we apply that?

Refer to the attached figure for description of the points.

BD and CE are perpendicular to AE.

So, in triangles ABD and ACE, angle A is common angle to both the triangles, $$\angle{ADB} = \angle{AEC} = 90$$ and $$\angle {ABD} = \angle{ACE}$$ (BD || CE)

Thus triangles ABD ad ACE are similar by AA (or angle -angle similarity theorem)

Thus, by similarity

AB/ AC = BD / CE

Given BD = 5 and AB = 0.5*AC

Thus CE = 10. Hence, Statement 2 is sufficient.

Per statement 1, x =30 does not provide us any other useful information.

Thus B is the correct answer.

Hope this helps.
Attachments

Similar triangles.jpg [ 11.3 KiB | Viewed 989 times ]

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Re: In the figure above, line AC represents a seesaw that is [#permalink]  25 Jul 2015, 05:33
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noTh1ng wrote:
What i don't get is why we can assume that the two triangles are similar just because AB = BC?

I mean it looks similar, but why can we apply that?

Attachment:

Untitled.png [ 21.95 KiB | Viewed 981 times ]

You can use three rules to prove that the triangles are similar.
1. AA- two angles are equal.
2. SSS- All three sides are proportional to each other.
3. SAS- One angle is equal and the two adjacent sides are proportional.

In this case, you know two angles are equal, x and the 90. Since the height of a point is being measured.

Hope it helps.
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Re: In the figure above, line AC represents a seesaw that is [#permalink]  25 Jul 2015, 06:25
thx akhilbajaj ; good for memorizing this stuff
Re: In the figure above, line AC represents a seesaw that is   [#permalink] 25 Jul 2015, 06:25
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