The weighing balance is of minimum number of weighings required to identify the heavier bag is

Question

There are eight bags of rice looking alike seven of which have equal weight and one is slightly heavier. The weighing balance is of minimum number of weighings required to identify the heavier bag is                                            

      (a) 2                                                                    (b) 3

      (c) 4                                                                    (d) 8