Mensuration Practice Test 6

Question : 33 of 40

Marks: +1, -0

If the area of the circular shell having inner and outer radii of 8 cm and 12 cm respectively is equal to the total surface area of a cylinder of radius

R_1

then the height of the cylinder well be:

${3R_1^2 - 30}/{7R_1}$
${R_1^2-40}/{R_1^2}$
${30-R_1}/R_1^2$
${40-R_1^2}/R_1$

Validate

Solution:

Area of circular shell =

π(R^2-r^2)

π(12^2-8^2)

π(144-64)

= 80π
Total surface area of a cylinder =

2πR_1(R_1+H)

80π =

2πR_1(R_1+H)

40 =

R_1(R_1+H)

40 =

R_1^2+R_1H

{40-R_1^2}/{R_1}

= H

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