A 5.5 g sample of a substance contains only carbon and oxygen. Carbon makes up 35% of the mass of the substance. The rest is made of oxygen. You are asked to determine the mass of oxygen in the sample. Which of the following expressions demonstrates a mathematical procedure to solve this problem using the proper order of operations? A 5.5 sample of a substance contains only carbon and oxygen. Carbon makes up 35 of the mass of the substance. The rest is made of oxygen. You are asked to determine the mass of oxygen in the sample. Which of the following expressions demonstrates a mathematical procedure to solve this problem using the proper order of operations? 100−(35/100)×5.5grams= ((100−35)/100)×5.5grams= 100−35/100×5.5grams= *Recall that to calculate a percent of an amount in grams means you have to convert the percent to a number and multiply by the amount in grams. For example, 50% means 50 out of 100, or 50 hundredths. So 50% of 10 grams is 0.50 times 10 grams. You need to take 0.50 and multiply it by 10 grams to determine 50% of 10 grams is 5.0. (50% and 10 grams are examples and not numbers for this problem.)

There are several ways you can do this. The equation above shows you subtracting 35% from 100% before you convert the result to a fraction. That is an appropriate expression for solving the problem.

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The other offered choices do not respect either the order of operations or the units of the problem. (The first and third choices are the same--both wrong.)

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