mathematical operations

**hebby** · December 21st 2009, 10:12 AM

how it is possible to remove the last three-digit of a number N using two mathematical operations

**Plato** · December 21st 2009, 10:28 AM

Originally Posted by hebby

how it is possible to remove the last three-digit of a number N using two mathematical operations

$\left\lfloor {\frac{N}{{1000}}} \right\rfloor$ ???

**tonio** · December 21st 2009, 10:34 AM

Originally Posted by hebby

how it is possible to remove the last three-digit of a number N using two mathematical operations

What kind of number is N? What three "last digits": from the right or from the left? What do you mean by "removing digits"?? What mathematical operations are allowed: sum, multiplication, power, taking logarithms...??
Common, some definitions!

Tonio

**hebby** · December 21st 2009, 10:59 AM

well that well only get u a decimal with all the digits still there

**hebby** · December 21st 2009, 11:00 AM

ya basically from the right....ie the last 3 digits....the operations u mentioned are all valid.....but a general method...to remove the last 3 digits from any number N

**hebby** · December 21st 2009, 11:01 AM

N= whole number...integer

**hebby** · December 21st 2009, 11:02 AM

eg) 12345=N and u end up getting 12....but minus last 3 divide by 100 is not valid as this can be applied once we know the numbers....but we actually dont know the number N

**tonio** · December 21st 2009, 02:47 PM

Originally Posted by hebby

ya basically from the right....ie the last 3 digits....the operations u mentioned are all valid.....but a general method...to remove the last 3 digits from any number N

No operations needed: if the number is $N=a_1a_2\ldots a_n\,,\,\,a_i\in\{0,1,2,\ldots,9\}$ , then take $N'=a_1\ldots a_{n-3}$

Or more seriously: take $\left[\frac{N}{1000}\right]$ , as already proposed by Plato.

Tonio

**hebby** · December 21st 2009, 02:52 PM

hey thanks, but how would the N divided by 1000 work? as you will end up with a number with decimals, how would you remove those?

**Plato** · December 21st 2009, 03:01 PM

Originally Posted by hebby

hey thanks, but how would the N divided by 1000 work? as you will end up with a number with decimals, how would you remove those?

Do you understand the floor function (greatest integer function)?
$\frac{{6346765}}{{1000}} = 6346.765\,\text{ so } \,\left\lfloor {\frac{{6346765}}{{1000}}} \right\rfloor = 6346$

**hebby** · December 21st 2009, 03:03 PM

no i never saw that before, but i can see how that would work now

**hebby** · January 5th 2010, 03:37 PM

Hi

I was think in the lines of

1) Multiply by 10^ -3

2) The we end up with a decimal, how can I remove the decimal from the integer?

Any ideas?

**Bingk** · January 5th 2010, 09:07 PM

I was thinking ... would the floor function be considered as an operation? Just curious about that

Could you also try ( N - ( N (mod 1000) ) ) / 1000? Basically, N minus the remainder when you divide by 1000, then divide that by 1000 ....

**hebby** · January 5th 2010, 09:10 PM

Could you show a numerical example on how that might work?

**Drexel28** · January 5th 2010, 09:17 PM

Originally Posted by Bingk

I was thinking ... would the floor function be considered as an operation? Just curious about that

Could you also try ( N - ( N (mod 1000) ) ) / 1000? Basically, N minus the remainder when you divide by 1000, then divide that by 1000 ....

$x-\{x\}=\lfloor x\rfloor$ . But, $\frac{N}{1000}-N\text{ mod }1000=\frac{N}{1000}-\left\{\frac{N}{1000}\right\}=\left\lfloor \frac{N}{1000}\right\rfloor$ . So, really all you've done is restate Plato's response.

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