Q. 7

# The base area of a right circular cone is 21m. and height is 14m. Let us calculate the expenditure to colour the curved surface at the rate of ₹1.50 per sq.m.

Answer :

Let, base radius of the cone = r m

According to problem,

⇒ πr^{2} = 21

⇒ r^{2} = 21 ×7/22

⇒ r = 2.58

∴ radius of the base = 2.58 m

Height of the cone = 14 m

∴ slant height of the cone,

= √(2.58^{2} + 14^{2})

= √(6.66 + 196)

= 14.24 cm

∴ curved surface area of the cone,

= πrl

= 22/7 × 2.58 × 14.24

= 115.47 sq. m

∴ Expenditure to colour the curved surface area,

= 115.47 × 1.50

= Rs. 173.2

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