Wooden blocks

[blackhole123]

Sorry if this riddle has already been posted.

 

You have eight wooden blocks. 7 have exactly the same mass, while 1 has slightly more. The difference is so slight, you cannot tell by touch and feel alone, and must rely on the very precise balance scale you have in front of you.

 

In only two measurements, how can you absolutely determine which of the 8 blocks is the odd one out?

[D H]

Is this a homework assignment, or are you just looking for an answer out of curiousity? If it is the former, you need to show some work on the subject.

[blackhole123]

No its just a riddle, I know the answer.

[Louise]

Take six blocks and place them on the scale, with three on each side.

 

Outcome A: Both sides of the scale are equal. Compare the remaining two to find the heavier block.

Outcome B: One side is heavier, take two blocks from the heavier side and weigh them. If one is heavier than the other, than you've found the heavier block. If they are both equal, then the remaining block out of the three is your desired block.

[D H]

Weigh three balls versus another three balls, then one ball against another ball. The choice of the balls for the first weighing is random. The choice for the second weighing depends on the outcome of the first:

• First weighing shows equal masses:
  Weigh the remaining two balls against each other. The odd ball is the heavier of the two.
  
• First weighing shows unequal masses:
  Weigh two of the three balls from the heavier group against each other. If the second weighing shows equal masses, the odd ball is the unselected ball in the heavier group. If the second weighing shows unequal masses, the odd ball is the heavier one.
  

[J.C.MacSwell]

Weigh three balls versus another three balls, then one ball against another ball. The choice of the balls for the first weighing is random. The choice for the second weighing depends on the outcome of the first:

• First weighing shows equal masses:
  Weigh the remaining two balls against each other. The odd ball is the heavier of the two.
  
• First weighing shows unequal masses:
  Weigh two of the three balls from the heavier group against each other. If the second weighing shows equal masses, the odd ball is the unselected ball in the heavier group. If the second weighing shows unequal masses, the odd ball is the heavier one.
  

 

Or just look at them. If one of the blocks is a ball you have found the odd ball.