Math with fractions – the best part of the imperial measurement system!

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No, no it’s not. Doing math with fractions requires focus and brain power. Things I’d rather not do because it makes me shift my thinking from whatever else I’m working on.

I don’t like changing gears (in my head) just to do some quick math.

I’d rather it be a thoughtless, simple process that is nearly impossible to screw up.

So I found a really cool trick to help add and subtract fractions, quickly, easily, without a calculator or an app, without requiring any real brain power or focus.

It requires a ruler, and a piece of paper.

When using this method, you’ll want to work with smaller numbers, so they fit on your ruler.

So if you’re needing to add something like 47-3/16″ plus 28-5/8″, you should just simply add the fractions alone with the methods outlined below. So 3/16″ + 5/8″. Then add that to the sum of 47 and 28. You follow me? Read it again if that didn’t make sense.

However, if you’re adding things like 4-3/16″ plus 2-5/8″, those are small enough, you don’t need to separate the whole numbers from the fractions.

So here’s what you do:

Adding – Lay a ruler on a piece of paper and mark a line at 0, and at the first number. Then move the ruler over so the 0 line of the ruler is in line with the mark you made at the first measurement. From here, mark a line at your second measurement.

Now move the ruler back to the starting point, and see where the second mark is on the ruler. 

That is the total sum of the 2 numbers. And you didn’t even have to find the common denominator!

Subtracting – Now that you have the concept, let me show you how to do subtraction with a demonstration.

I’m needing to find out how much is needed to make panel board 5-3/16″ wide, when the first piece I’m working with is 1-1/2″.

I could do the whole “math” thing and subtract 1-1/2″ from 5-3/16″.  But I don’t want to.

So instead, I’ll just put a couple marks on paper and let the ruler do the math for me: