Introduction: How to Multiply Decimals
Hi,
My mum's a teacher and she found thid really cool way of multiplying decimals in a teaching book. In the book it calls it 'Italian'.
Here goes...
Step 1: Table
In this example, the sum is 35.8 times 4.6
Set out a rectangle like this:
(The dots are decimal points)
(The diagonal lines are important)
Step 2: Tens
Multiply the numbers across so 3 times 4 is 12 and the tens digit is 10, so you write 1.
(If the product of the two numbers is less than 10, leave this half blank)
Step 3: Digits
Now, you must add the digits.
Step 4: Magic!
Add the up numbers diagonally. If the sum is over 10, carry one to the next sum to the left, if it is over 20, carry two to the left, etc.
Step 5: Decimal Point
Now, to find the decimal point, find the line where both decimal points join up and go along the line.
So the answer is 164.68!
Try with other numbers and enjoy "cheating" on your maths questions.
NM

Participated in the
3rd Epilog Challenge
13 Comments
7 years ago on Introduction
Very interesting, thanks for sharing this technique. This website has some multiplying decimals worksheets to practice with: http://stemsheets.com/math/multiplying-decimals-worksheet-horizontal
10 years ago on Introduction
YOU NEED MORE STEPS and examples
10 years ago on Introduction
Huh?
11 years ago on Step 3
"Now, you must add the digits."
I am not seeing any addition in this particular step.
11 years ago on Step 3
i dont understand.....
Reply 11 years ago on Step 3
Cool
11 years ago on Introduction
wow this is hard for me because im in 5th grade
11 years ago on Introduction
Explain the *pundent* square for integers
Reply 11 years ago on Introduction
*Huh*
Reply 11 years ago on Introduction
My teacher taught me this for mulitpying and dividing integers. example one positive and one negative make a negative, just follow the chart.
11 years ago on Introduction
OK Thanks
11 years ago on Introduction
I think it's COOL!
Reply 11 years ago on Introduction
Thanks