Exactly. Same kind of thinking gives you bounds on what can be done. For example, can you do 13 marbles in 3 weighings? 213 < 3^3, so maybe (though I think not)

Exactly. Same kind of thinking gives you bounds on what can be done. For example, can you do 13 marbles in 3 weighings? 213 < 3^3, so maybe (though I think not). Can you do 14 marbles? 214 > 3^3, so definitely no.