There are 8 bags of rice looking alike, 7 of which have equal weight and one is slightly heavier. the weighing balance is of unlimited capacity. using this balance, the minimum number of weighings required to identify the heavier bag is
a) 2
b) 3
c) 4
d) 8

Correct answer is A.

Split it up to 3, 3, 2.
 
Weigh the two 3's first.
 
If they balance, then the heavier one must be 1 of the 2 remaining.
If they don't then the take two of the 3 that was heavier and weigh them.
 
If they balance, then it's the one that's left.
 
If they don't then the heavier one is on the balance.