Each of four friends orders a sweatshirt from a catalog. There are 15 colors of

Mathematics
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Each of four friends orders a sweatshirt from a catalog. There are 15 colors of sweatshirts, 5 of which are all cotton and 10 of which are a blend. Each one orders a different color (no repeats) at random. What is the probability that the friends order only cotton sweatshirts?

a.11/5

b.1/5

c.12/65

d.1/273

Apr 29th, 2015

Each of four friends orders a sweatshirt from a catalog. There are 15 colors of sweatshirts, 5 of which are all cotton and 10 of which are a blend. Each one orders a different color (no repeats) at random. What is the probability that the friends order only cotton sweatshirts?

a.11/5

b.1/5

c.12/65

d.1/273

the probability is to select 4 cotton sweatshirts out of 15 sweatshirts, the way to select 4 cotton sweatshirts is 

4C5 = 5, pick up 4 sweatshirts randomly from 15 sweatshirts is 4C15, thus the probability is 

5/(15*14*13*12/4!) = 120/(15*14*13*12) = 10/(15*14*13) = 1/(21*13) = 1/273

 


Apr 29th, 2015

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