Read the following passage
howing passage and answer the questions given at the end :
Students of Class XII presented a gift to their school in the form of
an electric lamp in the shape of a glass hemispherical base surmounted by
a metallic cylindrical top of same radius 21 cm and height 3.5 cm. The top
was silver coated and the glass surface was painted red.
What is the cost of silver coating the top at the rate of 5 per 100 cm?
(11) What is the surface area of glass to be painted red? V
((i)
What
Rp 155
Answers
Rs 92.4 is the cost of silver coating the top , surface area of glass to be painted red = 2772 cm²
Step-by-step explanation:
a metallic cylindrical top of radius 21 cm and height 3.5 cm
Surface area = 2πrh + πr² ( as one surface merged with semi sphere)
= 2 (22/7) * 21 * 3.5 + (22/7)(21)²
= 462 + 1386
= 1848 cm²
cost of silver coating the top at the rate of Rs 5 per 100 cm²
=> Cost of silver coating per cm² = 5/100 Rs
=> Cost of silver coating of 1848 cm² = 1848 * 5/100
= Rs 92.4
the surface area of glass to be painted red
= 2πr²
= 2 (22/7)(21)²
= 2772 cm²
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