A CODE has 4 digits. You remember that the 4 digits are 1, 3, 5, and 7, but you cannot remember the sequence. What is the probability that you will guess the code correctly on the first try?
A)1/20
B)1/4
C)20/1
D)4/1

Question

michele_laino · Answer

Number n of total possibilities is:
$$n=4^{4}$$
so our probabilitie p, is:
$$p=\frac{ 1 }{ 4^{4} }$$

swissgirl · Answer

So in total there are 4*3*2*1 ways of entering these numbers
First time there are 4 choices Once you have chosen the first number the next one there will be 3 choices since you have already chosen one of the 4 numbers
So there are 24 ways of entering these numbers and there is only one choice
so there is 1/24 chance that you will enter correctly on the first try

swissgirl · Answer

@Michele_Laino you have to take into account that there cant be any repetition. There are 4 digits in the code and each one is entered once

michele_laino · Answer

@swissgirl  you are right!

swissgirl · Answer

Ya but .... why is 1/24 not an option -.-

anonymous · Answer

IDK, it is just what the book says...

swissgirl · Answer

ya lemme think abt it

anonymous · Answer

Thanks 4 helping. I think the book has an error

swissgirl · Answer

@ganeshie8 Can you check my work?

michele_laino · Answer

the number of permutations of a set composed by four numbers are 4!=24, so we can have only 24 possibilities

ganeshie8 · Answer

yeah it has to be 1/24

mostly its a printing mistake...

swissgirl · Answer

Thanks :)