 # NCERT Solutions Class 9 Mathematics Solutions for Surface Areas and Volumes - Exercise 13.4 in Chapter 13 - Surface Areas and Volumes

Find the radius of a sphere whose surface area is 154 \mathrm{cm}^{2} . \text { (Assume } \left.\pi=22 / 7\right)Let the radius of the sphere be r.

Let the radius of the sphere be r.

Surface area of sphere = 154 (given)

Now,

\begin{aligned} &4 \pi r^{2}=154\\ &r^{2}=(154 \times 7) /(4 \times 22)=(49 / 4)\\ &r=(7 / 2)=3.5\\ &\text { The radius of the sphere is } 3.5 \mathrm{cm} . \end{aligned}

Video transcript
"hello students welcome to lido q a video session i am sev your math tutor and question for today is find the radius of a sphere whose surface area is 154 centimeter square assume pi is equal to 22 by 7 let the radius of the sphere be r now as per the given question let the radius of the sphere be r surface area of the sphere if this is given is 154 centimeter square now what you need to do is apply the formula so formula for the surface area of the sphere is 4 pi r square and that is equal to 154 so need to find r square over here r square is equal to 154 divided by 4 pi value is 22 by 7 hence r square over here will be 49 upon 4 so from this we can get the value of r that is radius of the sphere r is then r is equal to 7 upon 2 so 7 upon 2 that means it is 3.5 hence the radius of the sphere is 3.5 centimeter and that is our final required answer if you have any query you can drop it in our comment section and subscribe to lido for more such q a thank you for watching"
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