Age 16 to 18 Challenge Level:
The pdf $f(x)$ of an exponential distribution with parameter
$$f(x) = \lambda \exp(-\lambda x)\quad x\geq 0$$
The cdf $F(x)$ of such a distribution is
$$F(x) = \int^x_0 f(x') dx'$$
Use your analytical skills to answer these questions:
1. Must the pdfs of two different exponential distributions
2. In what cases do $F(x)$ and $f(x)$ intersect?
3. Can the cdfs for two exponential distributions intersect?
4. Can the pdfs for three different exponential distibutions
intersect at the same point?
You might want to experiment with specific choices of $\lambda$
before constructing more general arguments.