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Mathematics

The ratio between the heights of two solid cones is 2 : 3 and ratio between their radii is 9 : 8. The ratio between their volumes is :

  1. 27 : 32

  2. 32 : 27

  3. 3 : 2

  4. 2 : 3

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Answer

Given,

Ratio between the heights of two solid cones is 2 : 3.

Let height of first (h1) and second cone (h2) be 2a and 3a.

Ratio between the radii of two solid cones is 9 : 8.

Let radii of first (r1) and second cone (r2) be 9x and 8x.

Vol. of 1st coneVol. of 2nd cone=13πr12h113πr22h2=r12h1r22h2=(9x)2×2a(8x)2×3a=81x2×2a64x2×3a=162x2a192x2a=2732=27:32.\dfrac{\text{Vol. of 1st cone}}{\text{Vol. of 2nd cone}} = \dfrac{\dfrac{1}{3}πr1^2h1}{\dfrac{1}{3}πr2^2h2} \\[1em] = \dfrac{r1^2h1}{r2^2h2} \\[1em] = \dfrac{(9x)^2 \times 2a}{(8x)^2 \times 3a} \\[1em] = \dfrac{81x^2 \times 2a}{64x^2 \times 3a} \\[1em] = \dfrac{162x^2a}{192x^2a} \\[1em] = \dfrac{27}{32} \\[1em] = 27 : 32.

Hence, Option 1 is the correct option.

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