Should be C - 5

Vol of cylinder = pi*r^2*h
8 and 10 are bigger nos so the cylinder will have max volume with diameter and height from these nos.

Now, you have to max out r^2*h and that would happen when diameter of cylinder is 10 and height is 8

So radius of cuylinder = 5

What's the OA?

I believe the answer should be 4.

The radius can never be 5 , since the cube always has one smaller side adjacent to the bigger side (10). And the max diameter would be the shorter side (8) .

OA please

ans is 4...
Raul..can u explain in detail....

wot i thot was...
volume of rectangular wooden box is 6*8*10 = 480

now volume of cylinder pi*r^2*h; taking h as max side = 10

so pi*r^2*h = 480
pi*r^2*10 = 480
r^2 = 48/pi
r approx is 3.1

so i selected 3
which is wrong...

Thanks raulverde. I got it

Consider each side at a time

1. Take 6x8 as a base and 10 as height. diameter cannot be more than 6.

vol of cylinder = pi*3^2*10 = 90pi

2. Take 8x10 as a base and 6 as height. radius = 4
vol = pi*4^2*6=96pi

3. Take 6x10 as a base and 8 as height. radius =3
Vol = pi*3^2*8=pi*72

radius for max volume = 4

I got stuck at this question too, but did not understand raul's point. Could someone please explain why radius can not be "5" ?

This is a OG 11 question and u can see the detailed ans there if u want. But to understand this picture a rectangular box with dimension 10*8*6, it can have rectangles with the following dimensions

10*8
10*6
8*6

If the radius of the cylinder is 5 its diameter is 10. Now picture keeping this cylinder with a diameter of 10 on a rectangular piece of paper with dimension of 10* 8. U will see the cylinder will come out from one side which measures 8 cms

For radius to be 5 u need at least one side to be 10* 10

Excellent ri2007. I understood it now! Thank you very much.