There are ten 50 paise coins placed on a table. Six of these show tails, four show heads. A coin is chosen at random and flipped over (not tossed). This operation is performed seven times. One of the coins is then covered. Of the remaining nine coins five show tails and four show heads. The covered coin shows.
a) a head
b) a tail
c) more likely a head
d) more likely a tail
Ans: a) a head
Assume that one coin, say the one showing a tail, is flipped 7 times instead of 7 different coins. Then it would show a head, and there should be 5 head and 5 tails. If by covering a coin, there are d5 tails and 4 heads to be seen, then the covered coin is a head. (verify that this argument holds even if 7 different coins are flipped.)
