Calculate the circumference of a right-angled triangle with legs 20cm and 15cm.

Since the radius of a circle circumscribed about a right-angled triangle is equal to half the length of the hypotenuse of this right-angled triangle, it is necessary to find the hypotenuse of this right-angled triangle.

Using the Pythagorean theorem, we find the hypotenuse of a given right-angled triangle:

√ (20 ^ 2 + 15 ^ 2) = √ (400 + 225) = √625 = 25 cm.

Therefore, the radius of the circle circumscribed about this triangle is 25/2 = 12.5 cm.

Knowing what the radius of the circle is, we can calculate its length:

2 * n * 12.5 = 25p cm.

Answer: 25p cm.