Solve the following problem.
Find the electric bill for 370 kwh's of electricity from Red River Region Co-op, which charges 0.094 dollars per kilowatt-hour with a surcharge of 0.005 dollars per kilowatt-hour and has a $28 facility charge. Do not calculate the sales tax.
The problem requires the multiplication of decimal fractions. We would need to multiply the total cost per kwh (0.094 + 0.005 = 0.099) by the number of kwh's used (370) and then add the facility charge (28). Since the cost per kwh is less than a whole dollar, the multiplication is the same as multiplying with fractions.
Notice that we could have completed the multiplication using the standard multiplication algorithm and then moving the decimal three places from the right in the answer. That is, we do not need to multiply decimals like we did fractions; we may multiply like we did with whole numbers.
Now by adding the facility charge we obtain the final bill 36.63 + 28 = 54.63. The total bill without sales tax for the 370 kwh's of electricity is $54.63.
This problem begins the motivation for the standard algorithm for multiplying decimal fractions where we count the number of place value positions to the right of the decimal point in the factors and use that value for the number of place value positions to the right of the decimal point in the product.
Find the electric bill for 370 kwh's of electricity from Lake Region Co-op, which charges 0.0959 dollars per kilowatt-hour with a surcharge of 0.0082 dollars per kilowatt-hour and has a $16 facility charge. Do not calculate the sales tax.
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Date last modified: June 30, 2010.
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By Kris Montis and Timothy Peil
