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'.
Teachers! Did you use this instructable in your classroom?
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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.
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