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?
((100 - 35)/100) x 5.5 grams =
100 - 35/100 x 5.5 grams =
100 - (35/100) x 5.5 grams =
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.)

Since ha sample contains 35% carbon which means (100-35)=65% is oxygen in the sample. In order to calculate the mass of oxygen in the sample we have to find the 65% of 5.5g which means we have to multiply 65/100=0.65 with 5.5g i.e 0.65*5.5. so the mathematical expression we use will be:

((100-35)/100) x 5.5grams=3.575grams of oxygen

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