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- three cubes of a metal whose edges are in ratio 3:4:5 are melted and converted into a single cube whose diagonal is 12root 3 cm find the edges of the three cubes .
- a right triangle ,whose sides are 15cm nd 20cm,is made to revlve about its hypotenuse. find the surface area of the double cone so formed.

*SOLUTION 1) *

Let the edges of the three cubes = 3*x*, 4*x* and 5*x*

Then,

Their volume

Given : The length of the diagonal of the single cube =

As we know that,

the length of the diagonal of a cube of side

⇒ edge of the single cube = 12 cm

Now,

Volume of the single cube = (12 cm)^{3} = 1728, cm^{3}

Since the three cubes are melted and converted into single cube

⇒ Sum of volumes of three cubes = volume of single cube

∴ The edges of the three cubes are 6cm, 8cm and 10 cm.

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