## Tuesday, January 4, 2011

### How many cubic feet is my washer?

I always enjoy the, "I get to use the math I learned in junior high!" moments because I can use these examples one day when my kids ask, "Why do I have to learn this?!" Here is a great use of measurement, formulas, and figuring out volume...

My washing machine broke. It is over 20 years old, so I decided it was probably time to start looking for a new one. I looked them up online and kept seeing how many cubic feet the new ones were. Well, how can I know how big that is if I don't know the cubic feet of my current washer? Hmmmm.... So I googled, "How many cubic feet is XXX washer?" I had written down the model number, serial number, brand and anything else I might need off the washer so I could find the information online. But what I found instead was (GASP!) how to calculate your cubic feet. Not only did I have to know what pi was, I needed to use the ol' formula A=pi (r squared). THEN I had to multiply the area by the height of the drum, to satisfy the formula V = pi (radius squared) (height) or V= pi X r^2 X h . But it doesn't end there! I measured in inches and ended up with the volume in cubic inches. In order to compare to the new washers, I needed to know how many cubic feet it was.

There are 12 inches in 1 foot, 144 (or 12x12) square inches in 1 square foot, 1728 (or 12x12x12) cubic inches in 1 cubic foot. So to find how many cubic feet you have, divide the number you got in inches by 1728. Then, you will know how many cubic feet your washer is in. Do yourself a favor and write it with permanent marker somewhere on the machine! It might come in handy at some point.

Figuring this out was an eye opener to me of the things we could ask children to figure out that will help them use what they are learning in math. My 4th grader isn't quite at the point of doing this, but one day... and I can't wait to show him! If you have other "using math" ideas, please share them!

P.S. My washer was 2.5 cubic feet!