I believe that the answer is 120 marbles.<span />
Answer:
The probability of picking two consecutive purple marbles without replacement is 14.72%.
Step-by-step explanation:
Initially, there are 4+6+2+8 = 20 total marbles.
The probability of picking a purble marble is
P_{1} = \frac{number of purple marbles}{number of total marbles}
P_{1}= \frac{8}{20} = 0.4
Since there are no replacements, there are now 19 total marbles, 7 of which are purple. So, the probability of picking another purple marble is
P_{2} = \frac{7}{19} = 0.368
The probability P of picking a purble marble(P_{1}), not replacing it, and then picking another purple marble(P_{2}) is:
P = P_{1}*P_{2} = 0.4*0.368 = 0.1472 = 14.72%
