Ratio - applied algenra problem

You could write the question
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.

Great thanks very much for your response

2x + 16x = 144

x = 8

8 * 16 = 128

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

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.

pepeprepa wrote:You could write the question
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