Question

Craft teacher of a school taught the students to prepare cylindrical pen holders out of card board. In a class of strength 42,if each child prepared a pen holder of radius 5cm and height 14cm, how much cardboard was consumed?

Answer 1

first we have to find the area of the circle and multiply its circumference by the height and add the both to get cardboard used for ONE pen holder.
∴(pi)(r²)
=(22/7)(5)
=110/7.
Now its circumference=(pi)(d)
=(22/7)(10)
=220/7.
It should be multiplied by height.
∴(220/7)(14)
=3080/7
Now Adding
(3080/7) + (110/7)
=3190/7.
now we have to multiply this by 42.
∴3190×42/7
=3190×6
=19140 cm
∴19140cm of cardboard was consumed.

Answer 2

No. of students = 42
Radius of holder = r = 5cm
Height of holder = h = 14cm
Now, 
Area of card board consumed = 42 x (curved surface area  of cylinder + area of base)
                                                 = 42 x (2 x $\pi$  x r x h + $\pi$                                                        x $r^{2}$
                                                 = 42 x (2 x 22/7 x 5 x 14 + 22/7 x 5 x 5
                                                 = 42 x (2 x 22 x 5 x 2 + 22/7 x 5 x 5)
                                                 = 42 x (440 + 550/7)
                                                 = 42 x (440 x 7 +550)/7
                                                 = 6 x 3630
                                                 = 21780 $cm^{2}$ ,, = Ans