How do you get 7 liters from 2 jars 5 liters and 4 liters?

Start with both empty: 0 in 5 litre jar, 0 in 4 litre jar

Fill 5: 5 in 5, 0 in 4

Pour from 5 into 4: 1 in 5, 4 in 4.

Empty out 4: 1 in 5, 0 in 4.

Transfer from 5 to 4: 0 in 5, 1 in 4.

Fill 5: 5 in 5, 1 in 4.

Pour from 5 into 4: 2 in 5, 4 in 4.

Empty out 4: 2 in 5, 0 in 4.

Transfer from 5 to 4: 0 in 5, 2 in 4.

Fill 5: 5 in 5, 2 in 4.

Done!