The Gateway to Computer Science Excellence
+12 votes

There are eight bags of rice looking alike, seven 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

  1. $2$
  2. $3$
  3. $4$
  4. $8$
in Numerical Ability by Boss (41.9k points)
edited by | 3k views

Simplest way to understand this question- 

minimum number of weighing required

what does it mean

3 Answers

+19 votes
Best answer
Answer is $a)$ i.e 2

 Divide in to $3-3-2$ and then take $3-3$ pair and then if they are equal then weigh the remaining $1-1$.


if out of $3-3$ one is heavier then take the heavier group and divide it $1-1-1$ take any two of these group and weigh again to get the heavier.
by Junior (833 points)
edited by
Can you explain the last line. According to me, even then we will have a total of 3 weighings.. How are you getting 2 for the worst case ?
I am also getting 3 weighing.
If 3 and 3 balances -> compare the other 2 and pick the larger one. If they don't balance, pick the heavier stack of 3 items. Weigh any two of them. If both are equal then the one left is the heavier one else pick the heavier one by observing the balance.

thankyou @krish  for clearing the doubt!

Can you please tell how to prepare for aptitude section because I am struggling in it.

amazing explanation piyush kapoor

What about the case 3 - 2 ???

+3 votes

remember in this types of question we always consider the worst case  in minimum terms

as we have 8 bags total so just divide it into equal parts

       (1st partition ) 4 bags and 4 bags then weigh balance (take out 4 bags whose have maximum weight)

then for that 4 bags again divide into 

   (2nd partition ) 2 bags and 2 bags then weigh balance (take out 2 bags whose have maximum weight)

then for that 2 bags again divide into 

 (3rd  partition ) 1 bag and 1 bag then weigh balance(so in the last anyone out of these two will heavier bag  )

by Active (3.3k points)
+3 votes
1. Take 3 bags and compare it with another 3 bags, if they are equal, then take remaining two bags and compare. Total wieghtings = 2.

2. If in step one, if 3 bags are not equal to another three bags. Then take the heavier 3 bag group and pick any 2 bags and compare , if they are same, then 3rd bag is heavy bag.If not, the we will get heavy bag anyway.

So, in either case only 2 wieghtings is required. Hence , Answer is A.
by Active (2.4k points)
Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true
50,737 questions
57,389 answers
105,434 users