Question

What is the perimeter of the shaded area?

I got 40cm but wasn't sure if it was correct or not.

Answer 1

Is the 5 cm the distance up the prism, or a length of one side of the shaded area?

Answer 2

If it is "up" I would think the perimeter would be 30........just a swag, without research.

Answer 3

It doesnt really say, all that I was given was "The shaded area in the diagram below shows the cross section of a square pyramid intersected by a plane parallel to the base. The pyramids edges are all 15 cm long."

Answer 4

If it is a side I would say it is 20 cm.

Answer 5

Then I would say they are saying the plane intersects half way up the 10cm slant height or at 5 cm.

Answer 6

What would that make the answer then?

Answer 7

Let me see, it is the base of a trapezoid whose sides are 5cm and the bottom base is 15 cm, but I don't know the angles. Let review for a moment.

Answer 8

Couldn't figure it out, but if it is linear decreasing from 15 to 0 over the 10 cm height, I would guess the side to be 15/2 at the halfway point (5 cm) so the permiter would be (15/2)*4=30, still just a swag.

Answer 9

ok, thanks for trying :)

Answer 10

Just realized something, there are two similar triangles. What is the total height (slant height) of the prism, is it 15 or 10 cm ?

Answer 11

I think now that it is 15, and using similar triangle proportions we get:
x:10 :: 15:15
15x=150
x=10
perimeter is 4x or 40 as you originally surmised. Still don't know what the height is, just assuming 15cm

Answer 12

@JiJi, see above, I think you had it correct all the time.