有兩條數學題吾識做……

17a )
Volume of cylinder = pi r^2 h = pi x (18^2) x (30) = 9720 pi cm^3
In each second, the pipe delivers 10 pi cm^3 water
Time required = volume of cylinder/rate of delivery
= 9720 pi/10 pi = 972 s = 16.2 min.

17b)
For 9 min., the pipe delivers 9 x 60 x 10 pi cm^3 water = 5400 pi cm^3 water
Let h be height of water in the tank
5400 pi cm^3 water = pi x (18^2) x h
h = 5400 pi cm^3 / pi x (18^2) = 16.6667 cm
Sorface area = pi x r^2 + 2 x pi x r x h = pi x 18^2 + 2 x pi x 18 x 16.6667 cm^2
= 324 pi + 600 pi cm^2 =pi x924 cm^2 = 2902.83 cm^2

6.
Volume of empty space in the cylinder = 20% of pi r^2 h = 0.2( pi x 7^2 x 20 cm^3) = 615,75 cm^3
number of stones = volume of empty space / volume of one stone
615,75 cm^3/ 64 cm^3 = 9.6
9 stones can be put into container.