Common Core: 6th Grade Math : Find a Percent of a Quantity as a Rate Per 100: CCSS.Math.Content.6.RP.A.3c

Study concepts, example questions & explanations for Common Core: 6th Grade Math

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Example Questions

Example Question #11 : Find A Percent Of A Quantity As A Rate Per 100: Ccss.Math.Content.6.Rp.A.3c

Red is a very popular car color. A production company manufactures cars and parks them in a lot behind the plant. There are \displaystyle 800 cars in the parking lot and \displaystyle 80\% of them are red. How many red cars are in the parking lot?

Possible Answers:

\displaystyle 640

\displaystyle 630

\displaystyle 460

\displaystyle 80

\displaystyle 360

Correct answer:

\displaystyle 640

Explanation:

We can use ratios and proportions to solve this problem. Percentages can be written as ratios. The word “percent” means for every hundred. In the problem, we are told that \displaystyle 80\% of the cars are red. In other words, for every hundred cars \displaystyle 80 of them are red. We can write the following ratio:

\displaystyle 80:100\rightarrow\frac{80}{100}

Reduce.

\displaystyle \frac{80}{100}\rightarrow \frac{8}{10}\rightarrow \frac{4}{5}

We know that there are \displaystyle 800 cars in the parking lot. We can write the following ratio by substituting the variable \displaystyle Red for the number of red cars:

\displaystyle Red:800\rightarrow \frac{Red}{800}

Now, we can create a proportion using our two ratios.

\displaystyle \frac{4}{5}=\frac{Red}{800}

Cross multiply and solve for \displaystyle Red.

\displaystyle 5 \times Red=4\times800

Simplify.

\displaystyle 5 Red=3200

Divide both sides of the equation by \displaystyle 5.

\displaystyle \frac{5Red}{5}=\frac{3200}{5}

Solve.

\displaystyle Red=640

There are \displaystyle 640 red cars in the parking lot.

Example Question #12 : Find A Percent Of A Quantity As A Rate Per 100: Ccss.Math.Content.6.Rp.A.3c

Red is a very popular car color. A production company manufactures cars and parks them in a lot behind the plant. There are \displaystyle 3200 cars in the parking lot and \displaystyle 8\% of them are red. How many red cars are in the parking lot?

Possible Answers:

\displaystyle 800

\displaystyle 256

\displaystyle 218

\displaystyle 182

\displaystyle 188

Correct answer:

\displaystyle 256

Explanation:

We can use ratios and proportions to solve this problem. Percentages can be written as ratios. The word “percent” means for every hundred. In the problem, we are told that \displaystyle 8\% of the cars are red. In other words, for every hundred cars \displaystyle 8 of them are red. We can write the following ratio:

\displaystyle 8:100\rightarrow\frac{8}{100}

Reduce.

\displaystyle \frac{8}{100}\rightarrow \frac{4}{50}\rightarrow \frac{2}{25}

We know that there are \displaystyle 3200 cars in the parking lot. We can write the following ratio by substituting the variable \displaystyle Red for the number of red cars:

\displaystyle Red:3200\rightarrow \frac{Red}{3200}

Now, we can create a proportion using our two ratios.

\displaystyle \frac{2}{25}=\frac{Red}{3200}

Cross multiply and solve for \displaystyle Red.

\displaystyle 25 \times Red=2\times3200

Simplify.

\displaystyle 25 Red=6400

Divide both sides of the equation by \displaystyle 25.

\displaystyle \frac{25Red}{25}=\frac{6400}{25}

Solve.

\displaystyle Red=256

There are \displaystyle 256 red cars in the parking lot.

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