I'm not sure how to solve this question without knowing the equation for failure of use in t... please help me?A statistical study indicates that the fraction of the electric toasters manufactured by a certain company that are still in working condition after t years of use is approximately $\displaystyle f(t) = e^{-0.2t}$.

a) What fraction of the toasters can be expected to fail before one year of use?

b) What fraction of the toasters can be expected to fail during the third year of use?

Here are the textbook answers...

a) 0.1812

b) 0.1215