There are 42 bags of rice looking alike, 41 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 ?

Question

There are 42 bags of rice looking alike, 41 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 ?

campbell_st · Answer

slip the bags on the scale 

21 on each side

which ever is heavier... that's where the bag is

next split the 21 into 10 and 10

if there are equal then the heaver bag of the 42 is the one left off the scales... 

so 2 weighings did the job