This is the important question in the exam point of view because this question was ask in 2014 cbse board exam.
Question from RS Aggarwal
Chapter Mensuration
Volume and surface
Volume and Surface Area of Solid
Exercise 17A
Page number 786
Deepak BoraNewbie
A 5-m-wide cloth is used to make a conical tent of base diameter 14 m and height 24 m. Find the cost of cloth used at the rate of 25 per meter.
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Let the slant height of the cone be ‘l’ meters.
height = 24 m
diameter = 14 m or radius = 7 m.
Then according to the question.
l² = h² + r²
l² = 24² + 7²
l² = 576 + 49
l² = 625
l = √625
l = 25 m
∴ the slant height of the cone is 25 m.
Curved Surface Area of the cone = πrl
= [22/7] × 7 × 25
Curved Surface Area of the cone = 550 m²
Now, length of the cloth used = Area/ width of the cloth
= 550/5
Length of the cloth used = 110 m
Cost of cloth = Rs. 25 per meter
Total cost of clothe used = 110 × 25
∴ Total cost of clothe used = Rs. 2750