Question

A medical researcher needs 7 people to test the effectiveness of an experimental drug. If 15 people have volunteered for the test, in how many ways can 7people be selected?

Answer 1

Given:

A medical researcher needs 7 people to test.

15 people have volunteered for the test.

To find:

We need to find a number of ways to select 7 from 15 people.

Explanation:

The number of ways to select 7 from 15 people can be found by the given formula.

$nC_r=\frac{n!}{r!(n-r)!}$

Substitute n=1`5 and r=7 in the formula.

$15C_7=\frac{15!}{7!(15-7)!}$

$15C_7=\frac{15\times14\times13\times12\times11\times10\times9\times8!}{7\times6\times5\times4\times3\times2\times(8)!}$

$15C_7=15\times13\times11\times3$

$15C_7=6435$

Final answer:

The number of ways = 6435 ways.