Question

Suppose a continuous random variable X is uniformly distributed with 0≤X≤20. What is P(0≤X≤5). Give a decimal answer

Answer 1

Judging by the given info, it sounds like the density function is
\[f(x)=\begin{cases}\dfrac{1}{20}&\text{for }0\le x\le20\\\\0&\text{otherwise}\end{cases}\]
The probability is given by the integral,
\[P(0\le X\le 5)=\int_0^5f(x)~dx\]
Alternatively, if you'd prefer a pre-calculus approach, you can consider the density function graphically:

The probability is the area of the shaded region.