There are 9 coins 8 are 1 gm and 1 are 2 gm , how will you find the heavier coin in minimum number weighing and how many weighing it will need?

3+3+3 coins...measure 2 sets..if they are equal then 2gm coin will be in 3rd set. and if they are unqual we will know the set containing 2gm coin. now again do the same process.. 1 coin in each side of the set containing 2gm coin. if equal then 3rd coin in 2gm coin n if not equal then we will know the coin by measuring .

In worst cases of luck it will take minimum 4 weighings. First divide 9 coins 4n5. Weigh one set to know which set has the 2g coin. If not lucky u may find 5 coins set having the 2g coin. Then divide it again 2n3. Weigh one set to know which set has the 2g coin. Again unlucky u may find the 3coins set having 2g coin. Then weigh two coins individually to know the 2g coin. Total 4 weighings.