self Maths Puzzle

ou have 9 balls, equally big, equally heavy - except for one, which is a little heavier.

How would you identify the heavier ball if you could use a pair of balance scales only twice?

Read Solution (Total 1)

Divide the 9 balls into 3 groups of 3. Compare the weight of two of those groups.

The heavier group should then be obvious, it will either tip the scales, or, if the scales stay balanced, then it is the group you didn't include.

Now, choose 2 balls from this group and compare their weights, and using the same logic as before, the heavier ball will be obvious.
8 years agoHelpfull: Yes(0) No(0)

self Other Question

You have 10 bags full of coins, in each bag are 1,000 coins.

But one bag is full of forgeries, and you can't remember which one.

But you do know that a genuine coins weigh 1 gram, but forgeries weigh 1.1 grams.

To hide the fact that you can't remember which bag contains forgeries, you plan to go just once to the central weighing machine to get ONE ACCURATE weight.

How can you identify the bag with the forgeries with just one weighing?

And what if you didn't know how many bags contain forgeries?
You have eight bags, each of them containing 48 coins.

Five of these bags contain only true coins, the rest of them contain fake coins.

Fake coins weigh 1 gram less than the real coins. You do not know what bags have fake coins and what bags have real coins. You can use a scale with precision up to 1 gram. Making only one weighing and using the minimum number of coins, how can you find the bags containing the fake coins?