5th Grade - Math

LESSON PROBLEM: Ratios and Percent: What are percentages? How do we use them to interpret facts and statistics about rice? How do we convert percentages into decimals and fractions?


STUDY GUIDE

PERCENT AND RICE

Ninety percent (90%) of the rice consumed in the United States is grown in the United States. The U.S. exports forty percent of its rice crop. Ten percent of the rice the U.S. consumes is imported from other countries. What does percent mean and how do we find out how much rice this is?

Percentage means part of a hundred. This mathematical term comes from the Latin phrase per centum, or per hundred. In mathematics, the symbol % is used to stand for percent.

A percent is a ratio whose second term is 100. A ratio is a way to compare two quantities like 90 out of 100. Because in this case the second number is 100, we can express this ratio as a percent, 90%.

Let's look at a few examples of ratios expressed as percents:

90 out of 100, or 90%

14 out of 100, or 14%

75 out of 100, or 75%

Percentage can also be converted to fractions and to decimals. Why would we want to convert percents to fractions or decimals? So we can solve problems using percents!

Percent Equation

Let's go back to our rice fact: If 90% of the rice we eat is grown in the United States, how much U.S. rice do we eat? The equation for finding an amount when we know the percent and total (called base in mathematics), is: Percent x base = amount. So, we would have to multiply the amount of rice consumed by 90% to solve this problem:

Say, 8,000,000 metric tons of rice were consumed in the United States, how much of it would be grown in the United States?

8,000,000 x 90% = ____________

In order to solve this equation, we need to do a conversion -- change percent into a fraction, or a decimal.

Percent to Fractions

To convert a percent to a fraction, you simply write it as the percent/100 and drop the percent sign. For example:

90% is 90/100

75% is 75/100

14% is 14/100

Once the percent is in the form of a fraction, with a numerator (top number) and a denominator (bottom number) of 100, you may also reduce the fraction by the greatest common factor, or the biggest number that will divide into both the numerator and the denominator. For example, 75/100 can be divided by 25 on the top and bottom and reduced to 3/4.

Percent to Decimals

Converting percents to decimals is easily done simply by removing the percent sign (%) and moving the decimal point two spaces to the left:
90% converts to .90.

75% converts to .75

14% converts to .14

150% converts to 1.50

Once we know how to convert percents, we are ready to look again at our original problem: How much U.S. rice do we eat if 90% of the rice we eat is grown in the United States?

90% of 8,000,000 metric tons =

90% converts to .90 x 8,000,000 = 7,200,000 metric tons of rice!

Or we could multiply by the fraction 9/10 (90% = 90/100, reduced to 9/10). Of course, the answer is still the same: 7,200,000 metric tons of rice.

Let's look at another rice fact:

If the United States trades 14% of the world's rice and the total rice traded is 16,000,000 (16 million) tons, how much rice does the United States trade?

14% of 16,000,000 is 14% x 16,000,000, or .14 x 16,000,000 = 2,240,000 tons of rice!

Knowing what percents are and how to convert them to fractions or decimals comes in handy when we are reading and studying about rice.




ACTIVITIES

Using the VOCABULARY words in this lesson, make and complete a crossword puzzle about percents.




EXTENDED LEARNING

Using what you have learned, answer the following questions:

1. What percent of the world trade in rice comes from the United States?

2. What percent of rice grown in the United States is consumed in the United States?

Now do some more research about U.S. rice production and trade and try to answer the following.

1. What percent of the value of agricultural production in the United States does rice represent?

2. What percent of the rice consumed in the United States is used directly for food (unprocessed)?

3. What percent of the United States rice plantings are long grain rice?

Express your answers to each question as percents, decimals and fractions.

ANSWERS: 14%, 90%, 1%, 62% and 71%

Now based on what you've learned, create three of you own percent problems that are related to rice production and trade.




VOCABULARY


  • percent
  • numerator
  • denominator
  • ratio
  • fraction
  • conversion


Click here to play Rice Rampage!
How is Rice Grown:
Farming rice is hard work. Click here to learn more about the Stages of Farming Rice.
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