Question

There are 7 acts in a talent show.

Answer 1

Answer:

• Event A: 1/35

• Event B: 1/840

Explanation:

Event A

For the event A, the order of the first 4 acts does not matter.

The number of different four acts taken from a set of seven acts, when the order does not matter, is calculated using the concept of combinations.

Thus, the number of ways that the first four acts can be scheduled is:

          $C(m,n)=\dfrac{m!}{n!(m-n)!}$

         $C(7,4)=\dfrac{7!}{4!(7-4)!}=\dfrac{7!}{4!(3)!}=35$

And the number of ways that four acts is the singer, the juggler, the guitarist, and the violinist, in any order, is 1: C(4,4).

Therefore the probability of Event A is:

           $P(A)=1/35$

Event B

Now the order matters. The difference between combinations and permutations is ordering. When the order matters you need to use permutations.

The number of ways in which four acts can be scheculed when the order matters is:

           $P(m,n)=\dfrac{m!}{(m-n)!}$

         $P(m,n)=\dfrac{7!}{(7-4)!}=P(m,n)=\dfrac{7!}{4!}=840$

The number of ways the comedian is first, the guitarist is second, the dancer is third, and the juggler is fourth is 1: P(4,4)

Therefore, the probability of Event B is:

            $P(B)=1/840$