An electronic device has an exponentially distributed lifetime, with an average of $5$ years. What is the period within which $5$% of the first to decompose, do so?
I know that $\lambda=\frac{1}{5}$ because the expected lifetime is 5 and its an exponential distribution
but i cant understand the question at all, is asking for quantile?
If it's an introductory material, then my interpretation agrees with yours, that the question is asking:
"What is the period within which $5$% of the devices decompose?"
It is worded in such a way to emphasize that the whole process is random, and we don't know which ones will decompose.
Thus the desired answer is the point where the exponential tail is $95$%, for the rate $\lambda = 1/5$ years.