Instructables
Picture of 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...
 
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Step 1: Table

Picture of 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

Picture of 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

Picture of Digits
Now, you must add the digits.

Step 4: Magic!

Picture of 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

Picture of 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
STEMsheets26 days ago

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

maxyor2 years ago
YOU NEED MORE STEPS and examples

HMice2 years ago
Huh?
Chaucermeow3 years ago
"Now, you must add the digits."

I am not seeing any addition in this particular step.
LiLGq3 years ago
i dont understand.....
NatNoBrains (author)  LiLGq3 years ago
Cool
nfk113 years ago
wow this is hard for me because im in 5th grade
MCzone3 years ago
Explain the *pundent* square for integers
NatNoBrains (author)  MCzone3 years ago
*Huh*
My teacher taught me this for mulitpying and dividing integers. example one positive and one negative make a negative, just follow the chart.
Punnett sqare.png
adamazing3 years ago
(removed by author or community request)
NatNoBrains (author)  adamazing3 years ago
OK Thanks
cokecola3 years ago
I think it's COOL!
NatNoBrains (author)  cokecola3 years ago
Thanks