The two coins i choose can be
A) FAIR - FAIR
B) FAIR - UNFAIR
C) UNFAIR - UNFAIR
NOTE : Here order doesnot matter, since i am choosing 2 balls (fair-unfair and unfair-fair both are same)
PROBABILITY (of getting both as heads)
= P(FF)*P(HH/FF) + P(FU)P(HH/FU) + P(UU)P(HH/UU)
= (4/7 * 3/6 * 1/2 * 1/2) + (4/7 * 3/6 * 1/2 * 1/3) + (3/7 * 2/6 * 1/3 * 1/3)