How to multiply fractions!
This instructable is an entry to the Burning Questions Round 6.5 contest.
The fraction images were generated using this site
Step 1: Multiplying Whole Numbers
To whole numbers we simply do this: (See image)
Step 2: Multiplying Fractions by Whole Numbers
The theory is the same for multiplying fractions by whole numbers(See image)
Step 3: Multiplying Fractions Together
To multiply fractions together you simply multiply both of the numerators(top numbers) together and both of the denominators (bottom numbers) together.(See image)
If necessary, remember to simplify your fraction!
Step 4: Cross-Cancelling
Cross cancelling is basically simplifying before you multiply, but, don't just simplify the fractions the normal way, instead cross-cancel. Cross-cancelling also makes it easier to multiply if using large numbers.
To cross-cancel the the multiplication 81/21 X 49/27,(See first image) try and divide the diagonals by the same number, e.g.
21 and 49 can both divide by 7, so we replace them with 3 and 7 respectively(See second image),
then we cancel the other diagonal, 81 and 27 can both be divided by 9, so we replace them with 9 and 3(See third image), then do the multiplication as in step 3. Remember that it doesn't matter if you can only cross-cancel in 1 direction.
The final answer to 81/21 X 49/27 is the improper fraction 63/9, in a mixed number that's 7/1 or just 7(See fourth image)