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    Subject

    Quantitative Aptitude

    Topic

    Areas & Volumes

    If the radius of a circle is decreased by 50%, find the percentage decrease in its area.

    ক)
    55%
    খ)
    65%
    গ)
    75%
    ঘ)
    85%

    Explanation

    Let original radius = R. New radius = 50100R\frac{50}{100}R = 50100R\frac{50}{100}R Original area = R2\frac R2 and new area = πR2\mathrm{πR}^2 3πR24∗1πR2∗100\frac{3\mathrm{πR}^2}4\ast\frac1{\mathrm{πR}^2}\ast100 Decrease in area = π(R2)2=πR24\mathrm\pi\left(\frac{\mathrm R}2\right)^2=\frac{\mathrm{πR}^2}4 = 75%

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