4. The volume of the rising water surface = the volume of the stone. It is known that the diameter of the bottom surface of a cylindrical water tank is 20cm, and the water level rises 1.5cm.

So the volume of the rising water surface =π×(20÷2)? × 1.5=47 1 cm3

5. Find the volume of the granary first: Step 1: The diameter of the granary is equal to the circumference÷π = 62.8÷3.14 = 20m.

Step 2: granary volume =π×(20÷2)? ×4= 1256 cubic meters

The corn is 75% full, so the volume of corn = 1256 cubic meters ×75%=942 cubic meters.

The weight of corn per cubic meter is 720kg, so the total weight of corn is 942× 720 = 678240kg.

One ton = 1000 Jin, so the corn weight of this granary is: 678240÷ 1000=678.24 tons.