make activity of product of decimal
Answers
Two students multiplied 0.2 by 0.4. Student 1 found a product of 0.8 and Student 2 found a product of 0.08. Which student had the correct answer? Explain.
Student 1 Student 2
Analysis: Let's convert each decimal to a fraction to help us solve this problem.
Factors Product
Fractions: x
=
Decimals: 0.2 x 0.4 = 0.08
If we multiply two tenths by four tenths, we get a product of eight hundredths.
Answer: Student 2 is correct since 0.2 x 0.4 = 0.08.
Example 1: Marina's car gets 44.8 miles per gallon on the highway. If her fuel tank holds 15.4 gallons, then how far can she travel on one full tank of gas?
Analysis: We can multiply 44.8 by 15.4 to solve this problem.
Step 1: Estimate the product.
Step 2: Multiply to find the product.
Multiply these decimals as if they were whole numbers. Ignore the decimal point.
Compensate by placing the decimal point in the product.
Step 3: Compare your estimate with your product to verify that your answer makes sense.
Our answer of 689.92 makes sense since the product of 44.8 and 15.4 ranges from 400 to 1,000.
Answer: Marina can travel 689.92 miles with one full tank of gas.
When multiplying decimals, placement of the decimal point is very important. Since there is one decimal digit in each factor, there must be two decimal digits in the product. This is because tenths x tenths = hundredths. Estimating the product lets us verify that the placement of the decimal point is correct, and that we have a reasonable answer. For example, if your product was 68.992 miles, then you would know that you made a multiplication error after comparing it with your estimate. Let's look at some more examples of multiplying decimals.