Question

A security system requires a five-digit passcode where each digit can be any number from 1 to 9. How many possible passcodes can there be?

Answer 1

Are you familiar with permutations?

Answer 2

partially
I know this equation c(n,r)=n!/(n-r)!r!

Answer 3

There are 15 employees that must attend training sessions where only 3 people can be trained at a time. How many different possible groups are there?

Answer 4

Yes use that formula. For your next questions you do not care for the arrangement as long as you have groupings, so you will use combinations.

Answer 5

ok so would it be 15!/(15-3)!3! ?

Answer 6

Correct.

Answer 7

The permutations for P, R, and Q are:

Answer 8

P, R, Q as the elements? What do you think?

Answer 9

(PRQ), (PQR), (RPQ), (QPR), (QRP), (RQP)

Answer 10

Correct. You you can also use the permutations formula.

Answer 11

ok thanks
There are 12,000 boys at a university of 28,000 people. If someone randomly knocks on a dorm room door, what are the odds that he will meet a girl?
for this on do I use the formula?

Answer 12

No this is probability. You want the probability of knocking a girl's door.

Answer 13

so I divide them and I get 2/3?

Answer 14

What do you mean by divide? You are given the number of boys. If you just take that value you will be calculating the probability of knocking a boy's door :)

Answer 15

so 3/7?

Answer 16

How did you get that value?

Answer 17

I don't really understand what you meant so I did 12,000/28000

Answer 18

Like I said, 12000 is the number of boys. If you use that value what you get is the probability for a boy's door.

Answer 19

The Fundamental Counting Principle is the most useful for describing:

Answer 20

combinations?

Answer 21

Not sure I think permutations. You should Google it

Answer 22

The Fundamental Counting Principle is the most useful for describing: