Mensuration
- If the radius of a circle is decreased by 10%, then the area of the circle is decreased by
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Using Rule 12,
Percentage decrease = 2x + x² % 100 = 2 × ( - 10) + (-10)² % 100
= (– 20 + 1)% = – 19%Correct Option: C
Using Rule 12,
Percentage decrease = 2x + x² % 100 = 2 × ( - 10) + (-10)² % 100
= (– 20 + 1)% = – 19%
- The outer circumference of a circular race-track is 528 metre. The track is everywhere 14 metre wide. Cost of levelling the track at the rate of Rs. 10 per sq. metre is :
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External radius of circular path = R metre
∴ 2πR = 528⇒ 2 × 22 × R = 528 7 ⇒ R = 528 × 7 = 84 metre 2 × 22
∴ In-radius (r) = 84 – 14 = 70 metre
∴ Area of path = π(R² – r²)= 22 (84² - 70²) 7 = 22 (84 + 70)(84 - 70) 7 = 22 × 154 × 14 = 6776 sq. metre 7
∴ Required cost = 6776 × 10 = Rs. 67760Correct Option: D
External radius of circular path = R metre
∴ 2πR = 528⇒ 2 × 22 × R = 528 7 ⇒ R = 528 × 7 = 84 metre 2 × 22
∴ In-radius (r) = 84 – 14 = 70 metre
∴ Area of path = π(R² – r²)= 22 (84² - 70²) 7 = 22 (84 + 70)(84 - 70) 7 = 22 × 154 × 14 = 6776 sq. metre 7
∴ Required cost = 6776 × 10 = Rs. 67760
- If the area of a square is increased by 44%, retaining its shape as a square, each of its sides increases by :
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Increase in each side = x% (let)
∴ 2x + x² = 44 100
If x = 20∴2x + x² = 2 × 20 + 400 = 44% 100 100 Correct Option: D
Increase in each side = x% (let)
∴ 2x + x² = 44 100
If x = 20∴2x + x² = 2 × 20 + 400 = 44% 100 100
- What will be the percentage increase in the area of a square when each of the its sides is increased by 10%?
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Percentage increase in area = 2x + x² % 100 = 2 × 10 + 10 × 10 % 100
= 21%Correct Option: D
Percentage increase in area = 2x + x² % 100 = 2 × 10 + 10 × 10 % 100
= 21%
- If the length and breadth of a rectangle are increased by 10% and 8% respectively, then the area of the rectangle increases by :
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Percentage increase in area = x + y + xy % 100 = 10 + 8 + 10 × 8 % 100 = 18 + 4 % = 18 4 % 5 5 Correct Option: B
Percentage increase in area = x + y + xy % 100 = 10 + 8 + 10 × 8 % 100 = 18 + 4 % = 18 4 % 5 5
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