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by shashank.ism » Mon Feb 08, 2010 7:03 am
If the length of the largest straight rod that can be put inside a cube is 10 m, then the surface area of the cube cannot be more than
a) 100 m2
b) 200 m2
c) 400 m2
d) 600 m2
e) Cannot be determined
Last edited by shashank.ism on Mon Feb 08, 2010 7:19 am, edited 1 time in total.
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by thephoenix » Mon Feb 08, 2010 7:09 am
200m^2

d(diag of cube)=10
d^2=(asqrt2)^2+a^2(a=side of cube)
--->3a^2=100
--->surface area of cube=6a^2=2*100=200
hence B
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by harsh.champ » Mon Feb 08, 2010 7:15 am
shashank.ism wrote:If the length of the largest straight rod that can be put inside a cuboid is 10 m, then the surface area of the cuboid cannot be more than
a) 100 m2
b) 200 m2
c) 400 m2
d) 600 m2
e) Cannot be determined
The straight rod have to be along the diagonal of the cuboid.[Though shashank,I think it will be cube not a cuboid otherwise we have to consider a lot of cases]

10=sqrt(x^2 + x^2 + x^2)
x=10/sqrt(3)
So, surface area will be [spoiler]6*(x^2) = 6x100/3 = 200[/spoiler]

HENCE, b.
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