Answer: B) 1/52
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Explanation:
Let's label the friends as A,B,C,D.
Person A has a probability of 7/16 when it comes to ordering a certain color of cotton sweatshirt.
Then 6/15 is the probability for person B. Note how the 7 and 16 drop by 1 for each. This is because no repeats are allowed. If person A goes for a blue sweatshirt, then person B cannot select blue as well.
Person C's probability is 5/14 and person D has a probability of 4/13
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So we have these fractions: 7/16, 6/15, 5/14, 4/13
Once again, we have the numerators and denominators counting down by 1 each time.
Multiplying those fractions gets us...
(7/16)*(6/15)*(5/14)*(4/13)
(7*6*5*4)/(16*15*14*13)
840/43680
(1*840)/(52*840)
1/52
So if you did 52 trials of this, then you should expect about 1 of those trials is where each friend orders a different color cotton sweatshirt.
1/52 = 0.0192 = 1.92% approximately
So this happens about 1.92% of the time.
