PUZZLEBOXX

FIRST CROSSING

If the farmer takes the fox, the chicken will eat the corn.

If the farmer takes the corn the fox will eat the chicken.

So, the farmer MUST take the chicken across to the market-side of the river.

SECOND CROSSING

The farmer crosses back to the farm-side on his own.

THIRD CROSSING

The farmer takes the fox across to the market-side - but he cannot leave the fox and the chicken together, so...

FOURTH CROSSING

The farmer brings the chicken back with him to the farm-side.  He leaves the chicken on the farm-side of the river but collects the corn.

FIFTH CROSSING

The farmer takes the corn across - which he safely leaves with the fox on the market-side of the river.

SIXTH CROSSING

The farmer returns to the farm-side alone.

SEVENTH CROSSING

The farmer collects the chicken and takes it across with him.  Now he has all three items on the market-side of the river and is on hand to ensure that they are kept safely apart.

That's a lot of rowing!  It might have been easier to build a bridge!