Question

Q. There are 8 bags of rice looking alike, 7 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
a) 2
b) 3
c) 4
d) 8

Answer 1

3? if it's 2, how?

Answer 2

a) 2

I think 2 because you put your first bag.. it weighs x pounds.. so then you put your second one and if the reading is more than 2x pounds then its the heaviest one.

Answer 3

But that's if you get lucky and your heaviest bag happens to be one of the first two that you put on a scale.

Answer 4

Or you put your first bag, it weighs x pounds, then you put your second one at it weighs less than 2x pounds. It means that the one that you put there first is the heaviest one, and the second one and all the others you have left are lighter.

Answer 5

oh... 2... I see...

Answer 6

I'm with what dpalnc said . It should be 3. Most obvious way is to weigh 4 one each side first, take the heavier 4, weigh 2 on each side, take the heavier, weigh 1 on each side. The heavier is the heaviest bag.

If you try weighing them one at a time, the minimum would be a single weighing, but in general, you won't get that.

Answer 7

split it up to 3, 3, 2. weigh the two 3's first. if they balance, then the heavier one must be 1 of the 2 remaining. if they don't then the take two of the 3 that was heavier and weigh them. if they balance, then it's the one that's left. if they don't then the heavier one is on the balance.

so two weighings is the answer.
nice problem...

Answer 8

I see now... Clever.

Answer 9

KingGeorge, I see what you mean, I agree. You are thinking about a balance, with two sides, I'm thinking about an electronic scale lol. On top of that, I'm thinking of getting lucky and getting the heaviest bag among the first two that you put on a scale )

Answer 10

Aaaa, i see now

Answer 11

I like this problem quite a bit.