Q. There are 6561 balls out of them 1 is heavy.find the minimum no of times the balls have to be weighted for finding out heavy ball

• for this type question ans is cube root of balls
  so ans=cube root(6561)=8
  so ans is 8
  
  explanation : make 3 groups of equal balls weight 2 groups
  if any group heavy so heavy ball in heavy groups
  if both weight equal then ball in third group and repeat procedure.........
• 10 years agoHelpfull: Yes(25) No(13)
• For problems like this, just find the 3rd root of the number. For ex: consider 3 balls, u can find the heavier by just weighing 2 balls, so min = 1. consider 9 balls, divide them into 3 equal groups, now u can weigh 2 groups to find the group in which the heavier ball lies, and u ll be left with 3 and u know how to find out of 3. so its 3 pow 2 = 9, then 3 pow 3 = 27...... 3 pow 8 = 6561. So the ans is 8.
• 10 years agoHelpfull: Yes(17) No(0)
• 6561 if u notice is 3^8...n can be divided by 3(prime factor) only...we keep on dividing it into sets of 3 and in 1 weighing itself you can determine which set is heavy. Divide that set into further 3 lots...keep doing that..
  6561
  2187 2187 2187 1st weighing
  729 729 729
  243 243 243
  81 81 81
  27 27 27
  9 9 9
  3 3 3
  1 1 1
  ANswer is 8 attempts
• 10 years agoHelpfull: Yes(12) No(0)
• 6561= 3^8
  
  so minimum 8 no of times the balls have to be weighted for finding out heavy ball.
• 10 years agoHelpfull: Yes(4) No(0)
• I know how to find it with 8 weighings. Since the number of balls exactly fits the maximum, I guess the author thought it too :-)
  
  You divide the balls in three equal groups and put 2 of them on the scales.
  If the scales are out of balance, the heavier ball is in the heavier group (kind of makes sense :-)
  If the scales are balanced, the heavier ball is in the 3rd group( the one not on the scales)
  discard the 2 unneeded groups and repeat the process
  
  in total it is needed to make log3 (6561) = 8 weighings
• 10 years agoHelpfull: Yes(4) No(1)
• Always find the cube root of the number for such types of problem
  cube root of 6561 is 8 and hence answer is 8
• 10 years agoHelpfull: Yes(3) No(0)
• 8. any ways :)
• 9 years agoHelpfull: Yes(1) No(0)
• 1 only , 6560/2 = 3285 ball will be on both sides .. if both having the equal .. the 1st boll which is not currently weighning down is the heaviest ..hence it wl take minimum one weight to judge it...
• 10 years agoHelpfull: Yes(0) No(11)
• 3^8=min 8 times to find in which grp amng 8 grps . again+2(to find which 1 is heavier in these 3)
• 10 years agoHelpfull: Yes(0) No(0)
• 3^8=6561 so ans=8
• 10 years agoHelpfull: Yes(0) No(0)