Question
If each edge of a cube is increased by 25% , then the percentage increase in its surface area is :
Answer: Option D
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Let original edge = a, Then , surface area = 6 `a^2`.
New edge = `125/100 a = (5a)/(4)`
New surface area = `6 xx ((5a)/(4))^2 = ( 150 a^2)/(16) = (75a^2)/(8)`
Increase in surface area = `((75a^2)/(8) - 6a^2) = (27a^2)/(8)`
`:.` Increase % = `((27a^2)/(8) xx (1)/(6a^2) xx 100)`% = 56.25% .
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