Cool math trick....?

Question

1. Grab a calculator (You won't be able to do this one in your head)
2. Key in the first three digits of your phone number (NOT the area code-if your number is 01-123-4567, the 1st 3 digits are 123)
3. Multiply by 80
4. Add 1
5. Multiply by 250
6. Add the last 4 digits of your phone number
7. Add the last 4 digits of your phone number again
8. Subtract 250
9. Divide number by 2

I know this ends up giving you your own telephone number but I still don't understand how it works. My algebra teacher gave us this and wanted us to write a small paragraph and explain how it works. Can someone please simplify it and clarify step by step how it works?

Answer 1

Let's call the first three digits of your phone number X, and the last 4 digits Y. So your phone number can be represented as 10,000X + Y. (The 10,000X moves the first three digits over four spaces, so they are followed by Y. For example if X is 123 and Y is 4567, your phone number is (10,000) * 123 + 4567, or 1,234,567. With me so far?)

Step 2: Start with X.
Step 3: 80X.
Step 4: 80X + 1.
Step 5: 20,000X + 250.
Step 6: 20,000X + 250 + Y.
Step 7: 20,000X + 250 + 2Y.
Step 8. 20,000X + 2Y.
Step 9: 10,000X + Y. Which as we saw above is your phone number.

Answer 2

Call the first 3 digits of your phone number x
Call the last 4 digits of your phone number y
There we go:
3) 80x
4) 80x + 1
5) 20000x + 250
6) 20000x + 250 + y
7) 20000x + 250 + 2y
8) 20000x + 2y
9) 10000x + y

Now if you multiply a number with 10000, you put 4 zero's behind it, so 123 * 10000 = 1230000
Adding y to this number (remember y has 4 digits) replaces the 4 zero's by y,
so 1230000 + 4567 = 1234567

Answer 3

45

Answer 4

Was going to work on this for you, but why don't you try figuring it out yourself? Are you going to get through your whole life like this?

Answer 5

Hey that's cool but I can't tell you how it works out that way.

Answer 6

I don't know how it works, but it is real cool.

Answer 7

I dunno