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Ratio - applied algenra problem

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by [email protected] » Mon Jul 21, 2008 12:08 pm
Hi

Can someone please help me understand the answer explanation to problem 97 in the Problem solving section of the OG 11. I have not typed the problem out but if you need me to just let me know.

thanks in advance
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by pepeprepa » Mon Jul 21, 2008 12:36 pm
You could write the question :wink:
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


We know that for every gram of hydrogen we have 8 grams of oxygen (that is the same as 2:16)
So we also know that in 9 grams of mass, there is 1 gram of H and 8 grams of O. So we understand that 8/9 of the mass is oxygen.
There are 144 grams of water.
We want the number of grams of oxygen in the 144 and we have the ratio of 8/9
We do: 144*8/9=128

D)128

Hope it helps you more than the book.
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by [email protected] » Mon Jul 21, 2008 1:14 pm
Great thanks very much for your response
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by AleksandrM » Mon Jul 21, 2008 2:30 pm
2x + 16x = 144

x = 8

8 * 16 = 128
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by malolakrupa » Thu Jul 24, 2008 9:16 am
Shoudnt the answer be 16 grams of oxygen , becuase in 9 grams of water there is 1 gram of oxygen and 8 grams of hydrogen. so in 144 grams of water there will be 144 / 9 grams of oxygen which is 16
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by shreyatagra » Mon Jun 20, 2011 7:59 pm
AleksandrM wrote:2x + 16x = 144

x = 8

8 * 16 = 128

Why a single variable for mass of 2 different components ?? Actually I also solved it this way, later realized I cannot take x for both Hydrogen and Oxygen.
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by Anurag@Gurome » Mon Jun 20, 2011 9:11 pm
malolakrupa wrote:Shoudnt the answer be 16 grams of oxygen , becuase in 9 grams of water there is 1 gram of oxygen and 8 grams of hydrogen. so in 144 grams of water there will be 144 / 9 grams of oxygen which is 16

It is just the reverse. In 9 grams of water, there is 1 gram of hydrogen and 8 grams of oxygen.
So, in 144 grams of water there will be (8/9) * 144 = 128 grams of oxygen.
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by MBA.Aspirant » Mon Jun 20, 2011 9:23 pm
pepeprepa wrote:You could write the question :wink:
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
H:O:Total
2:16:18
..: x: 144

x = 144*16/18= 128
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