To express the given set P in roster form, we simply list out all the natural numbers that are less than 11 in ascending order.
P = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
Now, let's express set P in set-builder notation. In set-builder notation, we define the properties or conditions that the elements of the set must satisfy.
P = {x | x is a natural number and x < 11}
In this notation, the variable "x" represents each element of the set, and the vertical bar "|" separates the variable from the condition or property it must satisfy. So, for set P, we state that each element "x" is a natural number and it must be less than 11.