05 Apr 04
This works for US Phone Numbers : Give it a try
Here is a math trick so unbelievable that it will stump you.
1. Grab a calculator. (You probably 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)
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 the number by 2
Does the answer ring a bell?
05 Apr 04
Originally posted by turtlexIt's not that unbelievable. 🙂
This works for US Phone Numbers : Give it a try
Here is a math trick so unbelievable that it will stump you.
1. Grab a calculator. (You probably 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)
3. Multiply by 80
4. Add 1
5. Multiply by 250
6. Add the last 4 digits of your ph ...[text shortened]... one number again.
8. Subtract 250
9. Divide the number by 2
Does the answer ring a bell?
Let A be the number equal to the first three digits of a seven-digit telephone number. Let B be the number equal to the last four digits of a seven-digit telephone number.
Here are the results of each step:
A
80*A
80*A + 1
250*(80*A + 1) =
20000*A + 250
20000*A + 250 + B
20000*A + 250 + 2*B
20000*A + 2*B
10000*A + B
Recall that A was defined as a three-digit number. Multiplying an integer by 10000 shifts the number left by four decimal places, effectively adding four 0s to the end of that number. This makes room for the final four digits to be added and the result is a seven-digit number equal to the source telephone number.
-Ray.