Question

answer the questions 15-25​

Answer 1

Answer:

15 - 25 is 10 it will make a number

Answer 2

Answer:

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15. The diameter of a football is 5 times the diameter of a cricket ball. Then the ratio of the surface area is.

Ans: option (d) 25:1

Let D and d be the diameter of football and cricket ball.

Now,radius of Football,R=

$\frac{D}{2}$

Now radius of cricket ball,r=

$\frac{d}{2}$

Now, D= 5d

=>2R=10r

R=5r

Now,

$\rm \: \frac{surface \: area \: of \: football}{surface \: area \: of \: cricket \: ball \: } = \frac{4\pi \: R {}^{2} }{4\pi \: r {}^{2} }$

$\rm \: = ( \frac{R}{r})^{2} = ( \frac{5r}{r})^{2} = \frac{25}{1}$

$\frac{25}{1} = 25:1$

25. The base radii of two right circular cones of the same height are in the ratio 3 : 5. Then the ratio of their volume is:

Ans: Option (b)

$\rm \: Let \:  r1 \:  and  \: r2 \:  be \: the \: radii \: of \: two \: cones \\ \rm \: and \:  V1  \: and  \: V2 \:  be \: their \: volumes. \\ \rm \: Let \: h \: be \: the \: height \: of \: the \: two \: cones . Then, \\ \rm \: V1 = \frac{1}{3}\pi \: r1^{2}h \: and V2=\frac{1}{3}\pi \: r2^{2}h$

Therefore,

$\rm \: \frac{V1}{V2} = \frac{r1^{2} }{r2^{2}} = \frac{9}{25}$

Hence, the ratio of the volumes of two cones is 9 : 25.