Ratio - applied algenra problem

karen.yodaiken@gmail.com · Posted: Mon Jul 21, 2008 1:08 pm Post subject: Ratio - applied algenra problem

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

pepeprepa · Posted: Mon Jul 21, 2008 1:36 pm Post subject:

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.

karen.yodaiken@gmail.com · Posted: Mon Jul 21, 2008 2:14 pm Post subject:

Great thanks very much for your response

AleksandrM · Posted: Mon Jul 21, 2008 3:30 pm Post subject:

2x + 16x = 144

x = 8

8 * 16 = 128

malolakrupa · Posted: Thu Jul 24, 2008 10:16 am Post subject:

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