"Mom, what's a common denominator?" 

Do you remember how to subtract fractions? Adding and subtracting fractions can be tricky. In conventional math, the first rule is that you can only add or subtract 'like quantities'.

So you can easily subtract 'thirds' from 'thirds' (2/3 - 1/3 = 1/3). Or you can add 'quarters' to 'quarters' (1/4 + 1/4 = 2/4) just as easily.

But this doesn't work if they're not 'like quantities'. You can't subtract 'thirds' from 'quarters' directly because they are not 'like quantities'. So 3/4 - 2/3 = 1/12, and not 1/4.

The Common Denominator is just a way to convert 'unlike quantities' into 'like quantities', so you can add or subtract them.

So let's see how we can subtract 1/4 from 1/3rd using conventional math and the least common demoninator. Then I'll show you a much faster way to do this without using math!

Superhero Mom explains Fraction Subtraction!

Mom shows junior the steps to subtract fractions using conventional math with a common denominator! But where is Junior? Good luck, Mom!

	First multiply the denominators (3 x 4 = 12). (Like Arnold...?) Stop that, I said DENOMINATOR not TERMINATOR!
	Then convert each fraction into 1/12ths. (Huh?)
	3/4 and 9/12 are equivalent fractions (multiply top and bottom by 3). (Mom, what's multiply?)
	And 2/3 and 8/12 are equivalent fractions also (multiply top and bottom by 4). (Why bother? Anyway, shouldn't we multiply by 3?)
	Now replace 3/4 by 9/12, and 2/3 by 8/12. (Mom, I'm hungry...)
	Now both terms (9/12 and 8/12) are expressed in 1/12ths. They are now 'like quantites', so we can at last subtract them. 9 - 8 = 1, so the difference is 1... careful, their difference is 1/12th. (Mom, I'm really bored and I'm hungry; please can we stop now!)

"Whew! Now here's how to subtract fractions with the Pizza Pursuits everyday math cards -- visually"

We can greatly simplify the steps to subtract fractions. We'll subtract 1/5 from 1/4 using the Pizza Pursuit cards.

	First place a 1/5 card on top of a 1/4 card.
	Offset cards and align the two ends of the 1/5 tag and the 1/4 tag.
	The start of the 1/5th tag marks their difference on the 1/4 card measure. But the exact answer isn't marked on the scale is it? So find another card and tag that matches.
	A number-20 card tag matches. The answer = 1/20th.

Junior: "Way to go, Mom. Subtracting fractions with Pizza Pursuits and visual math is real easy!" Mom: "You're welcome, junior!" Mom (aside): "Heh, this is amazing! 'Visual math' is oh so simple, even I can do it! I can't wait to tell my friends!"

You can use the Pizza Pursuits cards to visually subtract decimals, degrees and percentages too. It works just like fraction subtraction above.

Amaze your kids! Be a math wizard:

	Subtract mixed measurement system values, e.g. subtract 30° from 0.25 (1/6th).
	And you can subtract or add card groups just as easily. For example, subtract group A (1/12 + 1/6) from group B (1/12 + 1/5), and add group C (1/12 + 1/20).
	Overlay one group of aligned cards and tags on top of a second larger group of aligned cards and tags. Read group difference on the measure on the bottom card.

Visual math also works for addition or for addition and subtraction too!

Enjoy!