If you have 8 marbles and one is lighter than the rest, using a scale how would you figure out which one it is in two steps?

Question

Anonymous · Accepted Answer

Step 1: Select any 6 marbles. Place 3 marbles on each side of the scale. If one side goes up, go to Step 3. If they balance go to Step 2.

Step 2: Place the two remaining marbles on the scale. The marble that goes up is the light marble.

vStep 3: Using the 3 marbles that went up in Step 1, select any 2 marbles. Place one marble on each side. If one side goes up, that is the light marble. If they balance the other marble is the light marble

TV · Answer

pick 6 at random and measure 3x3.  If both groups eqaul, then lighter marble is one of the two remaining.  Measure those to get your lightest.  If 3x3 are unequal, take the lighter group, withdraw one at random, and measure the remaining two.  If they equal, then the wothdrawn one is the lightest, if not, the lighter one will be on the scale

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