A coin purse contains 9 nickels and 1 quarter. Two coins are drawn(adsbygoogle = window.adsbygoogle || []).push({}); WITH REPLACEMENT. What is the set S of this random experiment? What are the probabilities of the elementary events?

i'm a little confused by the "with replacement" concept. i'm just wondering if i'm doing it correctly. i have the equation n-1+k choose n-1 so here's my work:

set S = {two nickels, two quarters, one nickel and one quarter}

total possible ways of selection: (10-1+2) choose (10-1) = 55

P[two nickels] = (9-1+2) choose (9-1) / 55 = 45/55

P[two quarters] = (2-1+2) choose (2-1) / 55 = 3/55

P[one nickel and one quarter] = 1 - P_{all other events}= 1 - (45/55 + 3/55) = 7/55

have i done the problem correctly?

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# Probability with replacement

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