50 circular discs

When 50 circular disks are placed over each other, they form a cylinder with,

Radius, r = Radius of circular disc = 7 cm

Height, h = 50 × Height of each disk = 50(0.5 cm) = 25 cm

Also,

Total Surface area of cylinder = 2πr(r + h)

Where r is base radius and h is the height of cylinder.

Putting values, we get

Total surface area

Also,

Volume of cylinder = πr²h

Volume of given cylinder

When this cylinder is placed in a cubical box of side 25 cm

Space left = Volume of cubical box - Volume of cylinder

[Volume of cube = a³, where a is the side of cube]

Space left = (25)³ - 3850 = 15625 - 3850 =11775 cm³.