Question 1081622
P(urn 1)=(1/3) and probability urn 1 and red ball is (4/7)(1/3)=(4/21)
P(urn 2)=(1/3) and probability urn 2 and red ball is (5/8)(1/3)=(5/24)
P(urn 3)=(1/3) and probability urn 3 and red ball is (2/5)(1/3)=(2/15)
The sum of those probabilities has common denominator 21*15*24
numerator is 4*(15*24)+5(21*15)+2(21*24)/(21*15*24)
numerator is 1440+1575+1008=4023
denominator is 7560
probability is 0.5321 ANSWER
by adding 4/21(0.190) and 5/24 (0.208) and 2/15(0.133), one gets 0.531, but there is rounding error.