Friday, September 7, 2007

Fun with math

First off, let's get this video link out of the way.

Now that I've scared you all off, I'll get to the meat of this blog post, which is the oft-ignored 5-function pocket calculator.

I'm sure you're all familiar with what a 5-function calculator is. It's those really simple calculators that do addition, subtraction, multiplication, division, square root and percentage (and if you're paying attention, you'll notice that's 6 functions).

Everyone is pretty familiar with the basic functions. You press "1 + 2 =" and get 3, you press "5 x 6 =" and get 30, etc.

But what about the square root and percent keys? Or those "M+, M-, MRC" keys? Most people might never think to press those buttons, so let's take a look at what they do.

First up is perhaps the simplest key on the entire calculator: the square root key (that's the one that looks like a checkmark). It takes one number as its input, and spits out its square root. Let's try to apply that...

Let's say I want to mount a webcam in the top corner of my wall, but my computer is all the way down on the floor at the other end of the wall, we can use the pythagorean theorem to find out what length USB cable I need.

Since my wall is 12 feet wide and 8 feet tall, we punch in "12 x 12 =" and write down  "144", then type in "8 x 8 =" and write down "64", then we enter "144 + 64 =" and hit the square root key to get 14.4 and change, and resolve never to touch a calculator again because that was a royal pain in the ass to punch in.

But we can do better, if we use the calculator's built-in memory. First, we make sure that the memory is clear by examining the display for a little "M" icon that would indicate a stored value, and we begin. This time, we type in "12 x 12 M+" and the display indicates "144 M" showing us that it has remembered this value. Next we type in "8 x 8 M+", and the display shows "64 M". Next we hit the "MRC" button and magically the calulator shows us "208", which is the sum of 144 and 64. We hit the square root key and get the answer 14.4 and change again! Hooray!

But wait, we can still do better. On most 5-function calculators, the multiplication key has a hidden function: if we press the keys "12 x =" we see that the display indicates 144 without having to enter in the second 12! So now all we have to type is "12 x M+ 8 x M+ MRC" and hit the square root button and magically the result 14.4 is there plain as day!

Moving on, let's say you're out for dinner and you want to calculate what size tip to leave. The cheque comes out to $23.81 and you want to leave a 15% tip. How much money do you leave? Well just whip out your trusty calculator and press "23 . 81 + 15 %" and we can see that we should pay a total of $27.38.

Alternately, let's say you're shopping for a new TV, and you know that your friend can get you an 11% employee discount. You look at a model costing $1199 and you whip out your trusty calculator again, punching in "1199 - 11 %" and get $1067.11. But wait, what about the 13% combined sales tax? punch in "+ 13 %" and we see that the grand total is $1205.83, without the extended warranty. How much did that 11% save us? Punch in "1199 x 11 % + 13 %" and we get $149.04 (alternately, you could punch in "1199 + 13 % x 11 %" and get the same answer).

But let's not stop there, how about reciprocals? Like, what's 1/16th in decimal? As a percentage? Punch in "16 ÷ =" and you get 0.0625, punch in "16 ÷ %" and you get 6.25%. What percentage is 19/32nds? Punch in "19 ÷ 32 %" and we get 59.375%.

It's really worth spending a little time to get familiar with your calculator. You'll find that only having "5 functions" isn't very limiting at all, and you never know when knowing a few calculator tricks might come in handy.


Michelle said...

"Fun With Man" is the biggest misnomer ever. Ever.

noricum said...

Oooo... I learned something! I already was quite familiar with the memory keys, but wasn't as familiar with the hidden multiplication feature or the %. (And here I just thought it shifted the decimal place!)