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Water consists of hydrogen and oxygen, and the approximate [#permalink]
07 Dec 2012, 05:23

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Difficulty:

5% (low)

Question Stats:

81% (02:01) correct
19% (01:00) wrong based on 290 sessions

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?

Re: Water consists of hydrogen and oxygen, and the approximate [#permalink]
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.

Re: Water consists of hydrogen and oxygen, and the approximate [#permalink]
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?

Re: Water consists of hydrogen and oxygen, and the approximate [#permalink]
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 _________________

Re: Water consists of hydrogen and oxygen, and the approximate [#permalink]
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.

For my Cambridge essay I have to write down by short and long term career objectives as a part of the personal statement. Easy enough I said, done it...