help!! Probability questions! fan and medal!

Question

olsolneo123 · Answer

Jim has the security on his cellphone set so that he has to enter a code to unlock it.  His code consists of five numbers from 0 and 9.
Complete each of the following sentences regarding the probability of Jim correctly guessing his code.  Probabilities should be written in reduced fraction form.

If Jim forgot his code, but knew that he didn't use any number more than once, then the probability that he will guess the correct code on his first try is ______

If the code was comprised of only three numbers from 0 and 9 instead of five, which are never repeated, then the probability that he will guess the correct code on his first try is ______

amistre64 · Answer

how many digits are there for the first option?

olsolneo123 · Answer

i dont understand your question

xapproachesinfinity · Answer

ten digits? no

amistre64 · Answer

well, if you have to guess what a combination it, you have to enter a first number.  how many options do we have for that first number?

olsolneo123 · Answer

9?

amistre64 · Answer

10, 0 to 9 is ten digits

if no number is repeated, how many options are left for the second number?

olsolneo123 · Answer

9

xapproachesinfinity · Answer

no 8 options only since the first digit has 9 options

amistre64 · Answer

good, then 8, then 7 ...

we have 5 numbers to try so:

10*9*8*7*6 is how many we can attempt

xapproachesinfinity · Answer

oh my bad should be 9

amistre64 · Answer

this is called, 10 pick 5

olsolneo123 · Answer

so, i multiply those 5 numbers?

amistre64 · Answer

since there is only 1 correct code, then 1 out of 10 pick 5 seems reasonable.

amistre64 · Answer

yes, multiply them which is in accordance to the counting rule

olsolneo123 · Answer

i got 30,240

xapproachesinfinity · Answer

divid 1 by that to get the probability

amistre64 · Answer

there are 30240 ways to pick 5 elements from a set of 10, and only 1 of them is correct

olsolneo123 · Answer

i dont think that answers the question being asked

amistre64 · Answer

really?  how do we determine a probability of a given event?

amistre64 · Answer

spose we had 3 elements, and only a proper selection of 2 of them is the code

{abc}

ab
ac
ba
bc
ca
cb

there are 6 possible orderings of 2 picked form 3

3*2 = 6

1 out of 6 is correct

amistre64 · Answer

we have 10 elements, and need to pick 5

10 pick 5 = 30240,  and only one of them is correct

olsolneo123 · Answer

i appreciate your help. but my session became inactive, and i lost the question

olsolneo123 · Answer

so thanks anyway:)

amistre64 · Answer

good luck ;)

olsolneo123 · Answer

thanks