# Ex.11.3 Q8 Perimeter and Area - NCERT Maths Class 7

## Question

Find the cost of polishing a circular table-top of diameter $$1.6\rm\, m,$$ if the rate of polishing is $$\rm Rs.\, 15/\rm\,m^2.$$ (Take $$π = 3.14$$)

Video Solution
Perimeter And Area
Ex 11.3 | Question 8

## Text Solution

What is known?

Diameter of the circular table-top and the rate of polishing per meter.

What is unknown?

The cost of polishing a circular tabletop.

Reasoning:

To find the cost of polishing, first find out the area of the tabletop. To find the total cost of polishing, multiply the total area by rate of polishing per meter $$(\rm Rs \,15).$$

Steps:

Diameter of the circular tabletop $$= 1.6\rm\, m$$

Radius of the circular tabletop

\begin{align}=\frac{{1.6}}{2}\end{align}$$= 0.8\rm\, m$$

Area of circular table top

\begin{align}&=\pi {r^2}\\ &= 3.14 \times 0.8 \times 0.8\\ &= 2.0096\;\rm{m^2}\end{align}

Since, the cost of $$1\,\rm m^2$$ polishing $$= ₹\,15$$

$$\therefore$$ the cost of polishing

$$2.0096 \rm\,m^2 = 15 \times 2.0096 = ₹ \,30.14$$

Thus, the cost of polishing a circular tabletop is $$₹ \,30.14$$

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