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Water consists of hydrogen and oxygen, and the approximate

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Water consists of hydrogen and oxygen, and the approximate [#permalink] New post 07 Dec 2012, 05:23
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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
[Reveal] Spoiler: OA
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Re: Water consists of hydrogen and oxygen, and the approximate [#permalink] New post 07 Dec 2012, 05:26
Expert's post
Walkabout 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


Since the ratio, by mass, of hydrogen to oxygen is 2:16, then oxygen is 16/(2+16)=8/9 of mass of water.

Therefore there are 144*8/9=128 grams of oxygen in 144 grams of water.

Answer: D.
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Re: Water consists of hydrogen and oxygen, and the approximate [#permalink] New post 04 Jan 2013, 19:12
Walkabout 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


2 parts hydrogen 16 parts oxygen=18 Total parts

2x+16x=18x---->144/18, x=8 8*16=128 parts oxygen

D
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Re: Water consists of hydrogen and oxygen, and the approximate [#permalink] New post 02 Oct 2013, 10:37
Simplify the ratio of hydrogen, oxygen to total from 2:16:18 to 1:8:9. Divide total grams of water by the sum of the parts of the ratio to determine the approximate multiple of the ratio to use = 144/9=16

Finally apply factor to the part that is oxygen-----> 8*16=128
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Re: Water consists of hydrogen and oxygen, and the approximate [#permalink] New post 19 Dec 2013, 09:04
Walkabout 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



I solved this very sloppily.. 144/18 = 8... 8 * 16 = 80 + 48 = 128..

I do not know if this approach works in general (it even took me almost 4 minutes to solve it..), but it worked here.
Re: Water consists of hydrogen and oxygen, and the approximate   [#permalink] 19 Dec 2013, 09:04
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