Question 1166422
find probability draw fewer than 4 marbles to get a red one
for the first one red is 5/20=0.25
for the second one red is (15/20)(5/19)=0.1974
for the third one red is (15/20)(14/19)(5/18)=0.1535
for the fourth one red is (15/20)(14/19)(13/18)(5/17)=0.1174
That sum is 0.7883
Therefore, the probability it will require more than 4 draws is the complement or 0.2117

Draw 4 and get only 1 green
on the first (4/20) or 0.2
on the second (16/20)(4/19)=0.1684
on the third (16/20)(15/19(4/18)=0.1404
on the fourth (16/20)(15/19)(14/18)(4/17)=0.1156

That sum is the answer or 0.6244