Weighing Jelly Babies

Puzzles -> Measuring Puzzles

Real jelly babies have a mass of 10 grams, while imitation jelly babies have a mass of 9 grams.

Spike has 7 cartons of jelly babies, 4 of which contain real jelly babies, the others imitation.

Using a scale only once (and minimum disturbace of the boxes contents!), how can Spike determine which cartons contain real jelly babies?

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-\./^\./-

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