Multiplying Decimals : Multiplying Decimals A necessary life skill!
Why is this skill important? : Why is this skill important? If gasoline sells for $1.35 per gallon, what is the cost of 9 gallons of gasoline? Johann buys CDs for $7.50 each and sells them for $10.95 each. How much profit does he make on 20 CDs? If it costs $0.04 to write one check, what does it cost to write 150 checks?
How to multiply decimals : How to multiply decimals 1. Multiply the two numbers as if they were whole numbers. You ignore the decimals at this time. 2. Once you have the answer, count the number of decimal places to the right of the decimal point in BOTH numbers 3. Add the number of decimals places there are 4. Mark off that many decimal places in your number. Start at the right and count back Now lets try a few examples!
Example 1 : Example 1 1.46
x 8 1. Multiply the two numbers as if they were whole numbers. You ignore the decimals at this time. 2. Once you have the answer, count the number of decimal places to the right of the decimal point in BOTH numbers 3. Add the number of decimals places there are 4. Mark off that many decimal places in your number. Start at the right and count back 8 1 1 6 There are 2 numbers after the decimal point There are 0 numbers after the decimal point 4 3
Example 2 : Example 2 1. Multiply the two numbers as if they were whole numbers. You ignore the decimals at this time. 2. Once you have the answer, count the number of decimal places to the right of the decimal point in BOTH numbers 3. Add the number of decimals places there are 4. Mark off that many decimal places in your number. Start at the right and count back 1.4
X 2.5 0 2 7 0 8 2 + 0 5 1 3 There is 1 numbers after the decimal point There is 1 numbers after the decimal point
Slide 6: Example 3 1. Multiply the two numbers as if they were whole numbers. You ignore the decimals at this time. 2. Once you have the answer, count the number of decimal places to the right of the decimal point in BOTH numbers 3. Add the number of decimals places there are 4. Mark off that many decimal places in your number. Start at the right and count back .08
X .004 2 3 There are 2 numbers after the decimal point There are 3 numbers after the decimal point 0 0 0