Question

A bag contains 4 red and 6 blach balls O balls is drawn at random from the bag, its colour is observed and this ball along with two addibonal balls of the same colour are returnted to the bag, then the probabilaty then the drawn ball is red, is A. 310 B. 25 C. 15 D. 34 Select the correct answer from above options

Answer 1

Correct Answer - B Key idea Use the theorem of total probability Let E1= Event that first ball drawn is red E2= Event that first ball drawn in black A= Event that second ball drawn is rod P(E1)= 4 10 ,P( A E1 )= 6 12 ⇒ P(E2)= 6 10 ,P( A E2 )= 4 12 By law of total probability P(A)=P(E1)×P( A E1 )+P(E2)×P( A E2 ) = 4 10 × 6 12 + 6 10 × 4 12 = 24+24 120 = 48 120 = 2 5