Suppose 40 are all vats,

Then the big barrel 1 * * contains 40×5=200 kg more oil than the small barrel.

In fact, it's 32 kilograms more.

The difference is 200-32 = 168kg.

It is necessary to change some vats into smaller ones.

For every 1,

The total amount of oil in large barrels is reduced by 5 kg.

The total amount of oil in the keg has increased by 2 kilograms.

The difference between the total amount minus 5+2 = 7kg.

Need to change 168÷7=24.

That is, there are 24 barrels.

There are 40-24 vats = 16.