2. (42 *16)/15 = 44.8 (km)

Suppose: there are x kilograms of oil in a barrel.

When Party A pours 5 kilograms to Party B, if there is x-5 kilograms in barrel A, then barrel B has more 10 kilograms than barrel A, and barrel B has x-5+ 10=x+5 kilograms.

According to the meaning, A accounts for 80% of B, that is, (x-5)/(x+5)=80%.

Solution: x=45

A: In the past, a barrel of oil contained 45 kilograms.

4. If Party A and Party B are walking in opposite directions, and the sum of their speeds is 65+55 = 120km/h ... then the distance between the two places is120 * 4 = 480km.

Party A and Party B have the same amount of money. 80% of the money spent by Party A is 2:3. Assuming that the total amount of money is 1, then the money spent by Party B is 20%/(2/3)=30%.