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Answer 1 · 2017-10-24T10:47:56

#2/25, 9/100, 3/50# respectively

The bag contains in total #4 + 6 + 8 + 2 = 20# marbles.

The probabilities for each colour are as follows:

Blue: #4/20 = 1/5#

Red: #6/20 = 3/10#

Green: #8/20 = 2/5#

Yellow: #2/20 = 1/10#

For a probability of one thing followed by another, you simply multiply the two probabilities, so

#P("B then G") = 1/5 xx 2/5 = 2/25#

#P("R then R") = 3/10 xx 3/10= 9/100#

#P("Y then not G") = ?#

This last one is slightly trickier. The probability of something not happening is #1# minus the probability that it will happen, or

#P(barX) = 1-P(X)#

therefore

#P(barG) = 1-2/5 = 3/5#

so

#P("Y then not G") = 1/10 xx 3/5 = 3/50#