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## hydrogen to oxygen

grandh01 Master | Next Rank: 500 Posts
Joined
03 Jul 2012
Posted:
265 messages
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#### hydrogen to oxygen

Sat Aug 25, 2012 12:05 pm
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

OA is D

### GMAT/MBA Expert

Jeff@TargetTestPrep GMAT Instructor
Joined
09 Apr 2015
Posted:
867 messages
Followed by:
12 members
39
Fri Jun 26, 2015 8:58 am
grandh01 wrote:
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

OA is D
Solution:

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.

_________________
Jeffrey Miller Head of GMAT Instruction

Joined
09 Mar 2012
Posted:
166 messages
Followed by:
3 members
39
Target GMAT Score:
770
Sat Aug 25, 2012 1:06 pm
Here the H:O = 2:16 or 1:8

When you write in fraction, it means in every part there is one part Hydrogen and 8 parts Oxygen. So total parts are 1+8=9

Thus, H= 1/9 and O=8/9

Now, for the given 144gms of water, 144/9= 16gms of each part.

Oxygen has 8 parts out of 9 so 16*8 = 128 is the answer

OR you can multiply directly as 8/9(144)=128

Thus, ans= Option D

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