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The trapezoid shown in the figure above represents a cross

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Joined: 02 Dec 2012
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The trapezoid shown in the figure above represents a cross [#permalink]

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19 Dec 2012, 05:18
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The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5
[Reveal] Spoiler: OA
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Joined: 02 Sep 2009
Posts: 39597
Re: The trapezoid shown in the figure above represents a cross [#permalink]

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19 Dec 2012, 05:23
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The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5

Attachment:

Trapezoid2.png [ 9.67 KiB | Viewed 14297 times ]
The formula for calculating the area of a trapezoid is $$Area=\frac{1}{2}(base_1+base_2)(height)=\frac{1}{2}(2+5)(height)$$.

So, we need to find the height AC: $$AC=\sqrt{AB^2-BC^2}=\sqrt{13^2-5^2}=12$$.

Therefore, $$Area=\frac{1}{2}(2+5)*12=42$$.

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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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29 Aug 2013, 00:24
why AC is height here??? couldnt get it
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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29 Aug 2013, 01:51
nahianegmat wrote:
why AC is height here??? couldnt get it

Rotate the figure:
Attachment:

Untitled.png [ 6.29 KiB | Viewed 13302 times ]
Hope it's clear.
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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29 Aug 2013, 22:57
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Bunuel wrote:

The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5

Attachment:
Trapezoid2.png
The formula for calculating the area of a trapezoid is $$Area=\frac{1}{2}(base_1+base_2)(height)=\frac{1}{2}(2+5)(height)$$.

So, we need to find the height AC: $$AC=\sqrt{AB^2-BC^2}=\sqrt{13^2-5^2}=12$$.

Therefore, $$Area=\frac{1}{2}(2+5)*12=42$$.

You could save yourself some calculation here if you knew the pythagorean triple 5-12-13. That would shave a few seconds off of the problem.
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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30 Aug 2013, 00:02
Well I don't know the formula for calculating the area of trapezoid. Also, I like to solve sums without using paper pen and with few basic formulae.

I first found out the base (the bottomline in the question figure) using pythogoras triplet (5-12-13).
Then I imagined the figure as right-angled triangle sitting on top of a rectangle.
A(Triangle) = 1/2*3*12 +
A(Rectangle) = 2*12
Total = 42.
I don't know how to insert figures here so can't explain properly
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Joined: 08 Oct 2011
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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10 Sep 2013, 11:25
Attachment:
Trapezoid.png
The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5

If the trapezoid represents a cross section of the rudder of a ship, then the area of the cross section of the rudder in square feet should have been the area of both the triangles represented in the figure. I know I am obviously wrong here but the way I mentioned is stuck in my head.
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Posts: 39597
Re: The trapezoid shown in the figure above represents a cross [#permalink]

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11 Sep 2013, 02:54
aakrity wrote:
Attachment:
Trapezoid.png
The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5

If the trapezoid represents a cross section of the rudder of a ship, then the area of the cross section of the rudder in square feet should have been the area of both the triangles represented in the figure. I know I am obviously wrong here but the way I mentioned is stuck in my head.

That's not wrong at all. But the area of a trapezoid can also be found with the direct formula as shown in posts above. If you expand that formula you'll see that you basically get the sum of the areas of the two triangles.

Does this make sense?
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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11 Sep 2013, 04:57
Bunuel wrote:
aakrity wrote:
Attachment:
Trapezoid.png
The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5

If the trapezoid represents a cross section of the rudder of a ship, then the area of the cross section of the rudder in square feet should have been the area of both the triangles represented in the figure. I know I am obviously wrong here but the way I mentioned is stuck in my head.

That's not wrong at all. But the area of a trapezoid can also be found with the direct formulas as shown in posts above. If you expand that formula you'll see that you basically get the sum of the areas of the two triangles.

Does this make sense?

Oh right. Thank you. That is some relief definitely !
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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10 Jul 2014, 10:05
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See Image for half triangle + rectangle solution.
Attachments

Rudder.jpg [ 31.57 KiB | Viewed 10937 times ]

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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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03 Oct 2015, 15:22
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Re: The trapezoid shown in the figure above represents a cross [#permalink]

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23 Jun 2016, 09:28
Attachment:
Trapezoid.png
The trapezoid shown in the figure above represents a cross section of the rudder of a ship. If the distance from A to B is 13 feet, what is the area of the cross section of the rudder in square feet?

(A) 39
(B) 40
(C) 42
(D) 45
(E) 46.5

Although this problem may seem confusing based on the description of the shape, we must keep in mind that the diagram provided is simply a trapezoid. So when we are asked to determine the area of the “cross section of the rudder,” this really means "What is the area of the trapezoid?"

The formula for the area of a trapezoid is:

area = (base 1 + base 2) x height/2

The two bases are given as 2 feet and 5 feet. Because the height is always perpendicular to the base, the height of this particular trapezoid is the side that begins at A and ends at the right angle located at the bottom right of the figure. We don't know this value, so we must calculate it. We could use the Pythagorean Theorem to determine the height, but instead we note that we have a 5-12-13 right triangle, where the unknown side (or the height) is 12.

We can now substitute the values for the two bases (2 and 5) and the height (12) into our area equation.

area = (base 1 + base 2) x height/2

area = (2 + 5) x 12/2

area = 7 x 6

area = 42

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Re: The trapezoid shown in the figure above represents a cross   [#permalink] 23 Jun 2016, 09:28
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