A box contains 4 balls. 2 balls are drawn from it and are found to be white. The probability that all the balls in the bag are white is

IT CAN BE TAKEN 3 CASESE1;   2W+2NON WHITEE2;   3W+1  NON WHITEE3     4WP(E1)=P(E2)=P(E3)=⅓  P(4 white)=13.C2   4C2   413.C2   2C2   4+13.C2   3C2   4+13.C2   4C2   4                       =116+12+1                         = 35