For those who thinks they are really smart in math ... ?

Question

this is a math trick i just ain't able to resolve..

you can take a 4 digit number (4 different number) and add them and substract the result from the 4 digit number....

and all you have to do is give the first 3 numbers of the final result and i will give you the final....

here's an example:

if you take for example 4890,

4+9+8+0=21

->4890-21=4879

you will give 487 and i will figure out the 9;

please i need seious help

and thanks a lot

Answer 1

I don't understand. Can you please restate your question?

And how does this help you?

Edit:

Ok, I understand the process but what I don't understand it that you said that you needed help, but how are we helping you if we just give you some numbers and you figure out the last digit?

Answer 2

U made a mistake in subtraction, didn't U? It should be 4869.

It is silly. If you subtract the sum of digits from ANY number the result is divisible by 9.(Not necessarily 4 digits)

When you know 3 digits, remaining can be found out me

(NOT "figured out") by common sense.

Taken any n-digit number, do that oprartion and tell me all but last I can "find out" last.  

Answer 3

No you can't, since you can't know it: Start with 9560, subtract 20 (digit sum), you get 9540. Start with 9570, subtract 21 (digit sum), you get 9549. If You get the numbers 954, how will you know if it's 0 or 9? You can't.

@bskelkar: You had the right facts, but you got to the wrong conclusion. From the fact that a number is divisible by 9 "common sense" will not help you to distinguish between 0 and 9.