 # NCERT Exemplar Solutions Class 10 Mathematics Solutions for Surface Areas and Volumes - Exercise 12.4 in Chapter 12 - Surface Areas and Volumes

A factory manufactures 120000 pencils daily. The pencils are cylindrical in shape each of length 25 cm and circumference of base as 1.5 cm. Determine the cost of colouring the curved surfaces of the pencils manufactured in one day at Rs 0.05 per dm2.

The shape of pencil = cylinder.

Let the radius of base = r cm

Circumference of base = 1.5 cm

Circumference of circle is 2πr = 1.5 cm

r = 1.5/2π cm

According to the question,

Height, h = 25 cm

We know that,

Curved surface area of cylinder = 2πrh

Curved surface area of pencil = 2π (1.5/2π) 25 = 37.5 cm2

1 cm = 0.1 dm

1 cm2 = 0.01 dm2

37.5 cm2 = 0.375 dm2

Cost for coloring 1 dm2 = Rs. 0.05

Cost for coloring 0.375 dm2 (i.e. 1 pencil) = Rs. 0.01875

Cost for coloring 120000 pencils = 120000 ×0.01875

= Rs. 2250

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