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Water consists of hydrogen and oxygen, and the approximate

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by BTGmoderatorLU » Thu Aug 22, 2019 10:48 am

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Source: Official Guide

Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

A. 16
B. 72
C. 112
D. 128
E. 142

The OA is D
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by Brent@GMATPrepNow » Thu Aug 22, 2019 12:37 pm
BTGmoderatorLU wrote:Source: Official Guide

Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

A. 16
B. 72
C. 112
D. 128
E. 142

The OA is D
The ratio, by mass, of hydrogen to oxygen is 2:16
This means that, for every 2 grams of hydrogen, there are 16 grams of oxygen.
2 + 16 = 18
So, for every 18 grams of water 2 grams are hydrogen, and 16 grams are oxygen.
In other words, 16/18 of water is oxygen.
Simplify fraction to say: 8/9 of water is oxygen.

Approximately how many grams of oxygen are there in 144 grams of water?
Since we know that 8/9 of water is oxygen, we can write:
Weight of oxygen = (8/9)(144) = 128

So, there are 128 grams of oxygen in 144 grams of water.

Answer: D

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Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by swerve » Thu Aug 22, 2019 2:51 pm
BTGmoderatorLU wrote:Source: Official Guide

Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

A. 16
B. 72
C. 112
D. 128
E. 142

The OA is D
Given ratio \(= 2:16 = 1:8 =\) Hydrogen : Oxygen

Let the quantity \(= x\) (by mass)

\(x + 8x = 144\, \Rightarrow\, x = 16\)

Amount of Oxygen \(= 144-16 = 128\)

Therefore, the correct answer is __D__
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by Scott@TargetTestPrep » Sat Aug 24, 2019 4:19 am
BTGmoderatorLU wrote:Source: Official Guide

Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

A. 16
B. 72
C. 112
D. 128
E. 142

The OA is D
We are given that the ratio of hydrogen to oxygen in water, by mass, is 2 : 16. Using our ratio multiplier, we can rewrite this as 2x : 16x. We can now use these expressions to determine how much oxygen is in 144 grams of water.
2x + 16x = 144
18x = 144
x = 8

Since x is 8, we know that there are 16 x 8 = 128 grams of oxygen in 144 grams of water.

Answer D.

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