A probability density function for the lifetime t hours of Electra light globes is given by the rule:
f(t)=ke^(-t/200), t > 0
a) the value of the constant k
b) the probability that a bulb will last more than 1000 hours.
I understand how to complete part b of the question, however I need to answer a beforehand, and I have no idea even where to begin to find the answer.