Pls explain the answer of this question ..
Answers
SURFACE AREA of SPHERE : -
4 * pi * r ^2
where r is the radius of the sphere
CURVED SURFACE AREA of CYLINDER : -
pi * r^2 * h
where r is the radius of the cylinder and h is the height of the cylinder
ACCORDING TO THE QUESTION : -
Part (1)
Diameter of each sphere = 21 cm
So , radius of each sphere = 21 / 2 cm
= 11 . 5 cm
Surface area of each sphere =
4 * pi * ( 11. 5 cm ) ^2
= 4 * ( 22 / 7 ) * ( 21 / 2 ) * ( 21 / 2 )
= 1386 cm^2
Volume of eight such spheres
= 8 * 1386 cm^2
= 11088 cm^2
Cost rate of Silver paint = 25 paise / cm^2
Total cost of Silver paint
= 11088 cm^2 * 25 paise / cm ^2
= 277200 paise
= 2772 rupees
Part (2)
Radius of each cylinder = 1 . 5 cm
Height of each cylinder = 7 cm
Curved surface area of each cylinder
= pi r^2 h
= ( 22 / 7 ) * ( 1 . 5 ) * ( 1 . 5 ) * ( 7 )
= 49 . 5 cm^2
Curved surface area of eight such cylinders
= 8 * 49 . 5 cm^2
= 396 cm^2
Cost rate of Black paint = 5 paise / cm^2
Total cost of Black paint
= 396 cm^2 * 5 paise / cm^2
= 1980 paise
= 19 . 80 rupees
Total Cost overall
= 2772 rupees + 19 . 80 rupees
= 2791. 80 rupees