Guess your phone number

Guess your phone number

1.Grab a calculator (You won’t be able to do this one in your head)

2. Key in the first four digits of your phone number (for example the number is 0771234567 then 7123 is the first four number)

e.g 7123

3. Multiply by 80 e.g 7123*80=569840

4. Add 1 e.g 569840+1=569841

5. Multiply by 250 e.g 569841*250=142460250

6. Add the last 4 digits of your phone number e.g 142460250+4567=142464817

7. Add the last 4 digits of your phone number again e.g 142464817+4567=142469384

8. Subtract 250 e.g 142469384-250=142469134

9. Divide number by two e.g 2142469134/2

Do you recognize the answer? It is your number!142469134/2=71234567

 

Here is the explanation

Lets say phone number is xxxxyyyy

first 4 digits are xxxx0000/10000=xxxx

3. Multiply by 80

=xxxx*80

4. Add 1

=xxxx*80+1

5. Multiply by 250

=250(xxxx*80+1)
=20000*xxxx+250

6. Add the last 4 digits of your phone number

=20000*xxxx+250+yyyy

7. Add the last 4 digits of your phone number again

=20000*xxxx+250+yyyy+yyyy
=20000*xxxx+250+2*yyyy

8. Subtract 250

=20000*xxxx+250+2*yyyy-250
=20000*xxxx+2*yyyy

9. Divide number by 2

=10000*xxxx+yyyy
=xxxx0000+yyyy
=xxxxyyyy

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