# Math Help - mathematical operations

1. ## mathematical operations

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

2. Originally Posted by hebby
how it is possible to remove the last three-digit of a number N using two mathematical operations
$\left\lfloor {\frac{N}{{1000}}} \right\rfloor$???

3. 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

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

5. 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

6. N= whole number...integer

7. 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

8. 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

9. 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?

10. 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)?
$\frac{{6346765}}{{1000}} = 6346.765\,\text{ so } \,\left\lfloor {\frac{{6346765}}{{1000}}} \right\rfloor = 6346$

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

12. 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?

13. 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 ....

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

15. 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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