# 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?

2
by mbasavaraj

2016-01-20T20:13:01+05:30
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
(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.
you took area of circle as pi r^2 but later multiplied only one r
well thats what happens when u r in a hurry
u r wrong as well
can u pls specify where m  i wrong?
2016-01-20T20:13:03+05:30
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   x r x h +                                                         x
= 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  ,, = Ans