Treebeard's Stumper Answer 8 May 98

A Calculator Trick

Today is the 15th Dunn Middle School Science Fair! So here's a calculator trick that uses your age as well as your address (or zip code).

	1) Enter your address	93441
	2) Double it	186882
	3) Add 5	186887
	4) Multiply by 50	9344350
	5) Add your age (here 15)	9344365
	6) Add days in a year (365)	9344730
	7) Subtract 615	9344115

There's your address and age again, combined as one number! Why does this work?

Start with your address and age, and follow the steps with a calculator to end up with your address and age combined into one number. It's the same as multiplying your address by 100 and adding your age. Doubling and multiplying by 50 does the shift. Of course there are other steps to disguise this, but they all cancel out in the end. 5 times 50 is 250. Add 365 to get 615, and then subtract it in the last step. If x = address and y = age, then with some algebra we have:
50(2x+5)+y+365-615 = 100x+y.

Note: Here are all the steps as algebra:

	1) Enter your address (here x)	x
	2) Double it	2x
	3) Add 5	2x+5
	4) Multiply by 50	50(2x+5)
	5) Add your age (here y)	50(2x+5)+y
	6) Add days in a year (365)	50(2x+5)+y+365
	7) Subtract 615	50(2x+5)+y+365-615
	8) Simplify	100x+250+y+365-615
		100x+y+615-615
		100x+y

It's not hard to make up your own mathemagic tricks like this!

The Dunn Middle School Science Fair was a great success! We'll soon post abstracts of our projects on the DMS Homepage. My project was a Windows program for composing MIDI Drum tracks. It's available for download from Treebeard's Basic Vault.

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