Question

A pedestal is constructed in the form of frustum of a pyramid, the sides of the square ends of the frustum being 360cm and 160 cm and slant height 260cm. Find volume , lateral surface area including area of the top and the cost of construction @ rs.50 /cubic metre and plastering it @ rs.10 /square metre

Answer 1

If you draw a careful diagram, you will see that the altitude is 240cm between the bases.

Using similar triangles, you can see that if the pyramid were not chopped off, its height would be 320/3.

So, the missing part is a pyramid of base side 80 and height 400/3.

Now just work with the missing part and the retained part.

Then you can figure the cost.

Or, you can find useful formulas here

http://mathworld.wolfram.com/PyramidalFrustum.html