UPSC NDA Math Model Paper 10

If it is known that third toss gets head, the possible cases:
(H, H, H), (H, T, H), (T, H, H), (T, T, H)
∴ Total cases possible = 4
Total favourable cases = 3 [(H, H, H), (H, T, H), (T, H, H)]
So, required probability P=

Total favorable cases

Total possible cases

P=

3

4