It is given in the question that,
Diameter of circular garden = 21 m
∴ Radius of circular garden = Diameter/2 = 21/2 m
Now, the length of rope required for fencing the garden will be equal to the two times the circumference of the garden, because the fencing is done in 2 rounds.
And, One round of circle = the circumference of the circle = 2πr
= 22 × 3
= 66 m
Now, the gardener takes 2 rounds of fence.
⇒ Total length required = 2 × 66 = 132 m
Also, it is given that:
Cost of 1 m of rope = Rs 4
⇒ Cost of 132 m of rope = 4 × 132= Rs 528
∴ the total cost of the rope will be Rs 528
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A circular pond iNCERT - Exemplar Mathematics