Find the surface of the cuboid if two cubes of each 20cm edge are joined end-to-end?

Sure, let's solve this step by step:

1. First, we need to understand the shape we're dealing with. If two cubes of 20cm edge are joined end-to-end, we get a cuboid. The dimensions of this cuboid would be 20cm (height), 20cm (width), and 40cm (length).

2. The formula to find the surface area of a cuboid is 2lw + 2lh + 2wh, where l is the length, w is the width, and h is the height.

3. Substituting the given values into the formula, we get:

   2(20cm * 40cm) + 2(40cm * 20cm) + 2(20cm * 20cm)

4. Simplifying this, we get:

   2(800cm^2) + 2(800cm^2) + 2(400cm^2)

5. Further simplifying, we get:

   1600cm^2 + 1600cm^2 + 800cm^2

6. Adding these together, we get:

   4000cm^2

So, the surface area of the cuboid formed by joining two cubes of 20cm edge end-to-end is 4000cm^2.