(1) cylindrical oil drum, measured from the inside, with a bottom diameter of 40cm and a height of 50cm.

If 1 cubic decimeter can hold 0.85 kilograms of oil, how many kilograms can this oil drum hold?

Bottom radius: 40 ÷ 2 = 20 (cm)

Oil drum volume: 3. 14× 20× 20× 50 = 62800 (cubic centimeter) = 62.8 (liter)

Loadable diesel oil: 62.8× 0.85 = 53.38kg.

The seventh question-

The original volume of toothpaste used by each person every day is 3.14x (0.4/2) (0.4/2) x2 = 0.255438+02.

The original volume of toothpaste used in one year is 0.2512x365 = 91.688 cubic centimeter.

The volume of toothpaste used per person per day is 3.14x (0.5/2) (0.5/2) x2 = 0.3925.

At present, the volume of toothpaste used in one year is 0.3925x365 = 143.2625 cubic centimeters.

Everyone uses143.2625-91.688 = 51.5745 cubic centimeters more than before.

The reserved integer is about 52 cubic centimeters.