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**math9maniac****Member**- From: Tema
- Registered: 2015-03-30
- Posts: 407

Hi;

I came across this game or puzzle where your phone number tells your age. It's as follows:

1. Take the last digit of yourphone number.

2. Multiply it by 2.

3. Add 5 to the result.

4. Multiply by 50.

5. Add 1765 to the result.

6. Subtract your year of birth.

The result or final answer should be a-three-digit number. The magic is that, the first digit is your phone's last number, and the other 2, your age(in years, of course).

I realised though that even if you don't use the phone number as proposed, but any other number, that number will still be the first digit of your final answer.

I've tried it and it works, for others too. It's amazing. Now I want to know how this is possible. As in, I want an interpretation. Some time ago, I posted a similar puzzle and I had explanations for it. I want to know the magic behind the numbers and how such things come about or are created. Who knows, I may be creating some as well.

Many thanks for your usual cooperation and assistance.

math9maniac.

Only a friend tells you your face is dirty.

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,226

hi math9maniac

You can usually account for these number tricks with a bit of algebra.

Let's call the single digit you start with x.

Here are the steps:

2x

2x + 5

50.(2x+5) = 100x + 250

100x + 250 + 1765 = 100x + 2015

(note this is the current year)

Let's say you were born in the year 2000.

100x + 2015 - 2000 = 100x + 15( your age).

Note that 2015 - year of birth = your age for any person.

As x is a single digit, 100x will be a number of hundreds and the tens and units will be your age.

Bob

ps. If you were born in November 2000, then you'll only be 14 at this date, so, if you want to make sure the trick doesn't let you down, check if the person has had this year's birthday first.

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**math9maniac****Member**- From: Tema
- Registered: 2015-03-30
- Posts: 407

Hi bob bundy;

How do you do? Long time no see. Thanks for your kind response. I appreciate it. Based on your explanation, this game or puzzle still stands for next year only when the addend is changed to 1766. Is that correct?

Please have you come across any which works all round irrespective of what is the current year?

Many thanks again. Have a nice day.

Only a friend tells you your face is dirty.

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,226

hi math9maniac

Yes, you have to update the 1765 every year. And if you know your friend has a November birthday you can adjust the rules accordingly.

Why don't you make up your own; now you've seen how to do it?

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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I came across this game or puzzle where your phone number tells your age. It's as follows:

It is not a game. A game is a situation where self interested agents interact.

It is not a puzzle. A puzzle is a game with a dominant pure strategy

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**math9maniac****Member**- From: Tema
- Registered: 2015-03-30
- Posts: 407

Hi Bob;

Thanks again. I'll certainly come up with one and share it here for your opinion. But before then, I observed that most of these 'puzzles' happen to have the result where the age is always the last two digits, and the starting number rather, the preceding digits. Could it be the other way round, for a change or difference?

May I ask, could there be a similar 'puzzle' which still holds irrespective of the year or event?

Thank you.

math9maniac.

Only a friend tells you your face is dirty.

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,226

hi math9maniac

If you wanted the age to be in the hundreds place then you could start with that and times by 100 ( or 2, then 5, then 2 then 5 say, to make it more mysterious.

Here's one that'll always work.

Start by writing, in secret, a certain number** on a piece of paper and then seal it in an envelope. Show your audience, (three would be good) that the envelope will be in full sight throughout.

Ask someone to choose a single digit number; someone else another (different) and someone else a third (also different) . Ask them to make a three digit number from these. eg. They might choose 587

Tell them to reverse the digits (785) and subtract the smaller from the larger. (eg. 785 - 587 = 198)

If the result is only two digits (eg. 241 - 142 = 99) add a leading zero so it is three digits again (099).

I'll call this number x. Tell them to reverse the digits of x and add the result and x together, and write down their answer. Invite them to open the envelope to reveal that you correctly predicted this answer!

**Obviously, you have to know what to write down initially. This calculation will always result in the same answer so I'll leave you to discover what the 'magic' number is.

Can you figure out why this happens ?

Bob

ps. Agnishom. Neither a game nor a puzzle; this is magic!

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**math9maniac****Member**- From: Tema
- Registered: 2015-03-30
- Posts: 407

Hi Bob;

Thanks so much for your help. I do appreciate it.

Here's what I discovered:

And oh, I agree with you. This is no puzzle. It's magic; math magic.

Thanks again.

Yours ever grateful,

math9maniac.

Only a friend tells you your face is dirty.

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