Question 1185572
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4 R
2 G
2 Y
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8 total 

Without replacement: 

P(1st is G, 2nd is Y, 3rd is R) = (2/8)(2/7)(4/6) = 16/336 = 1/21

The 2/7 comes from the fact that only 7 remain after the first draw, and there are 2 Yellow so 2/7 represents the probability of a favorable 2nd draw outcome.  Similar for 3rd factor relating to the draw of Red.

With replacement:

In this case, the denominator stays constant at 8, as we are replacing after each selection:  P(G, Y, R) = (2/8)(2/8)(4/8) = 16/512 = 1/32
Qualitatively, this makes sense: say we pick G on 1st draw.  Since we are replacing that G into the urn, it slightly reduces the probability of selecting a Y on the 2nd draw.  Similar for R on 3rd draw.