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## OG 16 Data Sufficiency Question 86

This topic has 3 expert replies and 0 member replies
Mseemab Newbie | Next Rank: 10 Posts
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#### OG 16 Data Sufficiency Question 86

Sun Mar 19, 2017 2:27 am
Elapsed Time: 00:00
• Lap #[LAPCOUNT] ([LAPTIME])
Hi there everyone,
Can anyone help with the below question please? I don't get how the second equation is sufficient.. :/

A tank is filled with gasoline to a depth of exactly 2 feet. The tank is a cylinder resting horizontally on its side, with its circular ends oriented vertically. The inside of the tank is exactly 6 feet long. What is the volume of gasoline in the tank?

(1) The inside of the tank is exactly 4 feet in diameter.

(2) The top surface of the gasoline forms a rectangle that has an area of 24 square feet.

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GMATGuruNY GMAT Instructor
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Sun Mar 19, 2017 4:15 am
Mseemab wrote:
Hi there everyone,
Can anyone help with the below question please? I don't get how the second equation is sufficient.. :/

A tank is filled with gasoline to a depth of exactly 2 feet. The tank is a cylinder resting horizontally on its side, with its circular ends oriented vertically. The inside of the tank is exactly 6 feet long. What is the volume of gasoline in the tank?

(2) The top surface of the gasoline forms a rectangle that has an area of 24 square feet.

In the figure above, C is the center of the left circular base and rectangle RSTU is the surface of water.
Since the area of RSTU = 24, and it is given that ST=6, RS=4.
Since C is the center of the circular base, CV is a radius that bisects RS into two lengths of 2.

CV:
The figure indicates that CV is equal to the sum of x and and the height of the water (2).
Since CV is a radius, we get:
r = x+2
x = r-2.

Red triangle:
In the red triangle, x and 2 are legs and CS is both the hypotenuse of the triangle and the radius of the cylinder.
Thus:
x² + 2² = r².

Substituting x=r-2 into x² + 2² = r², we get:
(r-2)² + 2² = r²
r² - 4r + 4 + 4 = r²
8 = 4r
r = 2.

Thus, the height of the water -- 2 -- is equal to the radius of the cylinder.
Since the height of the water is equal to HALF the diameter, the volume of the water is equal to HALF the volume of the cylinder.
Since we can calculate the volume of the cylinder using r=2 and h=6, the volume of the water can be determined.
SUFFICIENT.

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Thanked by: Mseemab
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GMATGuruNY GMAT Instructor
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Sun Mar 19, 2017 6:16 am
Mseemab wrote:
Hi there everyone,
Can anyone help with the below question please? I don't get how the second equation is sufficient.. :/

A tank is filled with gasoline to a depth of exactly 2 feet. The tank is a cylinder resting horizontally on its side, with its circular ends oriented vertically. The inside of the tank is exactly 6 feet long. What is the volume of gasoline in the tank?

(2) The top surface of the gasoline forms a rectangle that has an area of 24 square feet.
An alternate approach:

RULE:
If points A, B and C are not collinear and are all the same distance from point O, then points A, B and C lie on a unique circle with center O.

In the figure above, AB is the diameter of the left circular base and rectangle RSTU is the surface of water.
Since the area of RSTU = 24, and it is given that ST=6, RS=4.
Since AB is the diameter of the circular base, AB bisects RS into two lengths of 2.

Since points R, S and B are all equidistant from point O, points R, S and B lie on a unique circle with center O.
Implication:
O is the center of the left circular base, on which lie points R, S and B.

Thus, the height of the water -- 2 -- is equal to the radius of the cylinder.
Since the height of the water is equal to HALF the diameter, the volume of the water is equal to HALF the volume of the cylinder.
Since we can calculate the volume of the cylinder using r=2 and h=6, the volume of the water can be determined.
SUFFICIENT.

_________________
Mitch Hunt
GMAT Private Tutor
GMATGuruNY@gmail.com
If you find one of my posts helpful, please take a moment to click on the "Thank" icon.
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Jay@ManhattanReview GMAT Instructor
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Sun Mar 19, 2017 10:07 pm
Mseemab wrote:
Hi there everyone,
Can anyone help with the below question please? I don't get how the second equation is sufficient.. :/

A tank is filled with gasoline to a depth of exactly 2 feet. The tank is a cylinder resting horizontally on its side, with its circular ends oriented vertically. The inside of the tank is exactly 6 feet long. What is the volume of gasoline in the tank?

(1) The inside of the tank is exactly 4 feet in diameter.

(2) The top surface of the gasoline forms a rectangle that has an area of 24 square feet.
Hi Mseemab,

Let's discuss statement 2 only.

We have a rectangle of area = 24.

It is given that the height of the cylinder = 6, thus 24 = 6*Cord; Cord -> the horizontal line of gasoline within the circular ends of the cylinder

We know that the depth of gasoline = 2 feet. We can draw a right-angled triangle within a vertical circular end and calculate the radius of the circle. It would come out to be 2 feet, implying that the cylinder is half-filled. Now we can calculate its volume. Sufficient.

Hope this helps!

Relevant book: Manhattan Review GMAT Data Sufficiency Guide

-Jay
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Thanked by: Mseemab

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