Answer :

Given that, radius of the circular lid of a tank, r = 1.4 m

Now this lid is painted on both sides. So, we need to find area of both sides of the circular lid.

Area of one side = πr^{2}

= 22/7 × 1.4^{2}

= (22 × 1.4 × 1.4)/7

= 43.12/7

= 6.16

Area of both sides = 2 × Area of one side

= 2 × 6.16

= 12.32

So, area painted on both sides of 1 circular lid = 12.32 m^{2}

Then, area painted on both sides of 100 such circular lid = 12.32 × 100 = 1232 m^{2}

Cost of painting 1 m^{2} area = Rs. 20

Cost of painting 1232 m^{2} area = 20 × 1232 = Rs. 24640

Thus, it will cost Rs. 24,640 to paint 100 such lids at the rate of Rs. 20 per m^{2}.

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