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Name: Connie
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Question:
I have a combination lock with four places, each has the number possibility of zero to nine. I want to know how many possible numbers combinations can fit (example 0000,0001 thru 9999). Also where on the web would there be a calculator that could answer this for me? Besides you guys!!



Replies:
Since all normal digits are used, there are 10000 possible combinations. Calculate it by taking the number of possibilities in the first spot, 10, times the number in the second (10), the third, and fourth: 10*10*10*10 = 10000.

There isn't really any special calculator needed.

Trying all the combinations--just count from 0 to 9999--is fairly easy to do with such a lock. With only 10000 combinations, it can be done in a few hours.

Thanks,
Eric Tolman
Computer Scientist


Hello,

The first digit can be 0 to 9, i.e., 10 different numbers. The second digit can also be 9, so you have 10 x 10 =100 combinations (0 to 99) with two sets of numbers. And so on. With four sets of digits you would have a total of 10,000 combinations (including 0000).

You would not need a calculator for this one.

Can you think of a possible combination that is not in the 0 to 9999 range? The answer is no.

Good luck.

Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory


Connie,

If I read your question correctly, you ask how many four digit combination numbers can be produced using digits 0 through 9. If so, this can be easily determined by looking at the possibilities:

0000 <--- possibility # 1
0001 through 9999 <--- 9999 more combination possibilities

This gives a total of 10,000 combination of four-digit numbers using the digits 0 through 9.

A way to calculate this is by N**x where N is the number of digits possible (here, 10 different digits are possible) 0 through 9 and x is the number of places available (here we have 4 places available for a 4 digit number)

note the formula is N raised to the x power

meaning, 10**4

or 10 X 10 X 10 X 10 = 10, 000 combinations

another example: how many combinations are available using digits 0-3 for a 2 digit number

the possibilities are: 00 01 02 03 10 11 12 13 20 21 22 23 30 31 32 33 or 16 possibilities

the formula would tells us:

N**x is 4**2 or 4 x 4 = 16

Thanks for using NEWTON!

Richard R. Rupnik
Internal Quality Auditor
Lucent Technologies


Actually you just answered you own question by seeing that the numbers went 0000, 0001,....9999. you can go from 1 to 9999 plus the option for zero. This means you have 9999 + 1 possible combinations or 10,000 possible combinations. Look in an elementary statistics book to get a better idea about combinations and permutations. This will give you equations that you can use on just about any calculator.

BTW, a quick way to figure this is that you have 10 possible numbers (0-9) to use in 4 different places. Therefore, the number of combinations is 10^4 = 10,000. If you had only 2 numbers to use (0 or 1) in 4 different places, the number of combinations would be 2^4 = 16. This 2 number system, or binary system, is the basis for computers and calculators everywhere.

C. Murphy


The easy answer to your question is to think of each possible combination as a number (which they are). For example, 0000 is zero, 0001 is one, 0020 is twenty, and so on. How many numbers can you make that correspond to different combinations? 10,000. These are 0001 to 9999, and then 0000 for the last, so 9999 + 1 = 10000.

This doesn't need a calculator, don't you agree?

Richard Barrans Jr., Ph.D.
Chemical Separations Group


Nice part of the world you live in. Pretty. Green.

There are 10 possibilities for the first number in the combination, right? For EACH of these numbers, there are 10 possibilities for the second number, giving a total of 10 x 10 = 100 possible combinations of 1st and 2nd numbers. Proceeding logically, there are 10^4 = 10,000 combinations for 4 places. Another way to see this quickly is from your notation above ("0000,0001 . . . 9999"). Pretty clearly, the available combinations form the numbers between 0 and 9999. How many such numbers are there? Ten thousand, natch.

If you are thinking of picking the lock, you can see you have a problem. But all is not lost: cheap combination locks will sometimes open if you are close but not exactly on the right numbers. That is, if the first number ought to be 1, the lock will often open if you dial in 2 or 0, or possibly even 3 or 9. If the lock will open when you dial in the right number +/- 1, then you actually only have 4 numbers per place (because 1 will work for 0,1,2, 4 will work for 3,4,5, 7 will work for 6,7,8, and then 9 works for 9, gee). There would then be only 4^4 = 256 combinations to try.

You can also try pulling on the shaft while rotating the wheels (if it looks like I think it does). Usually one of the wheels will be holding up the shaft a little more than the others. If you feel very carefully as you turn the wheels, you may feel the shaft move slightly out when you hit the right number of that particular wheel. Continuing in this process, you may be able to pick the lock.

Grayce



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