How many ways can you buy 2 DVDs from a display of 15?

Reese Estes
2022-05-09
Answered

How many ways can you buy 2 DVDs from a display of 15?

You can still ask an expert for help

verrainellewtzri

Answered 2022-05-10
Author has **13** answers

Step 1

We assume that someone will not buy two of the same DVD.

For the first DVD, there is a choice of 15 , but once the first is bought, there is a choice of 14 for the second one.

There are $15\times 14$ choices $=210$.

Step 2

However, this does not take order into consideration .... the 2 DVD's might be the same, just bought in a different order, so we need to divide this number by 2 to avoid the duplicates.

$\frac{210}{2}=105$

We assume that someone will not buy two of the same DVD.

For the first DVD, there is a choice of 15 , but once the first is bought, there is a choice of 14 for the second one.

There are $15\times 14$ choices $=210$.

Step 2

However, this does not take order into consideration .... the 2 DVD's might be the same, just bought in a different order, so we need to divide this number by 2 to avoid the duplicates.

$\frac{210}{2}=105$

Jaime Coleman

Answered 2022-05-11
Author has **3** answers

Step 1

Assumption: choosing $a+b$ is classified the same as choosing $b+a$.

This is the condition of 'combinations'

Step 2

$\Rightarrow {{.}}^{n}{C}_{r}\to \frac{n!}{(n-r)!r!}$

$\Rightarrow {{.}}^{n}{C}_{r}\to {{.}}^{15}{C}_{2}\to \frac{15!}{(15-2)!2!}$

$=\frac{15\times 14\times \overline{)13!}}{\overline{)13!}{.}2!}=\frac{15\times 14}{2}$

$=105$

Assumption: choosing $a+b$ is classified the same as choosing $b+a$.

This is the condition of 'combinations'

Step 2

$\Rightarrow {{.}}^{n}{C}_{r}\to \frac{n!}{(n-r)!r!}$

$\Rightarrow {{.}}^{n}{C}_{r}\to {{.}}^{15}{C}_{2}\to \frac{15!}{(15-2)!2!}$

$=\frac{15\times 14\times \overline{)13!}}{\overline{)13!}{.}2!}=\frac{15\times 14}{2}$

$=105$

asked 2021-08-19

Let X represent the difference between the number of heads and the number of tails obtained when a coin is tossed n times.

What are the possible values of X?

What are the possible values of X?

asked 2021-08-20

Let X be a normal random variable with mean 12 and variance 4. Find the value of c such that P{X>c}=.10.

asked 2021-08-19

Based on the Normal model N(100, 16) describing IQ scores, what percent of peoples

asked 2022-02-11

Giving a test to a group of students, the grades and gender are summarized below

A | B | C | Total | |

Male | 19 | 12 | 10 | 41 |

Female | 5 | 8 | 14 | 27 |

Total | 24 | 20 | 24 | 68 |

If one student is chosen at random,

Find the probability that the student was female OR got an "C".

asked 2021-11-16

Interest centers around the life of a concrete mixer. Let A be the event that the concrete mixer fails a test, but B be the event that the concrete mixer displays strain wears but does not actually fail. Event A occurs with probability 0.20, and event B occurs with probability 0.35.

a)What is the probability that the concrete mixer does not fail the test?

b)What is the probability that the concrete mixer works perfectly well (i.e., neither displays strain nor fails the test)?

c)What is the probability that the concrete mixer either fails or shows strain in the test?

a)What is the probability that the concrete mixer does not fail the test?

b)What is the probability that the concrete mixer works perfectly well (i.e., neither displays strain nor fails the test)?

c)What is the probability that the concrete mixer either fails or shows strain in the test?

asked 2021-12-18

Two fair dice are rolled. Find the joint probability mass function of X and Y when (a) X is the largest value obtained on any die and Y is the sum of the values; (b) X is the value on the first die and Y is the larger of the two values; (c) X is the smallest and Y is the largest value obtained on the dice.

asked 2021-09-07

A box contains 50 balls, exactly ten of them are red and
the others are black.

If five balls are chosen at random from the box knowing that the first two balls are red, what is the probability that the third one is black?

If five balls are chosen at random from the box knowing that the first two balls are red, what is the probability that the third one is black?