There are 50 large and small barrels of fruit juice, each with 4 kg, and each with 2 kg. As we all know, there are more big barrels than small ones.
Suppose there is a vat. There are 50 vats.
4A-2(50-A)=80
A=30
∴50-A=50-30
=20
There are 30 big barrels and 20 small barrels.