3) If boys and girls are equally likely, then out of 600 families of 3 children, the number of families having all girls is :

probability of a family having all girls = 1 / 2^3 = 1/8

 which is equal to 75 / 600

so 75 families.

If you meant drawing a white ball from second bag is it 29/63?

There are two possibilities:white or black

4) One bag contains 4 white and 5 black balls. Another bad contains 6 white and 7 black balls. A ball is transferred from the first bag to the second bag. The probability that the ball drawn is white is :

Prob. of white ball being transferred = 4/9

Prob. of black ball being transferred = 5/9

Prob. of white ball drawn from 2nd bag -:::---->

Case 1 white transferred:

7 white 7 black so 1/2

Case 2 black transferred :

6 white 8 black so 6/14 = 3/7

Total prob = (4/9) (1/2)    +  (5/9)( 3/7)

= 2/9 + 5/21 =  14 + 15 / 63

 = 29/63