Statistics - What is the probabillity it last another 25 hours if it has already lasted 40 hours?

Given the following





probability a battery lasts at least 40 hours is 0.95


probability it lasts at least 65 hours is 0.7.





What is the probability that it lasts at least another 25 hours, given that it has already lasted 40 hours?

Statistics - What is the probabillity it last another 25 hours if it has already lasted 40 hours?
Naturally, the way to do this problem is to use conditional probablities. P(it lasts 65 hrs | it lasts at least 40 hrs) = P(it lasts at least 40 hrs and it lasts at least 65 hrs)/P(it lasts at least 40 hrs). But obviously, it must have lasted at least 40 hours if it lasts 65 hours. So the probability is .7/.95 = (7/10)/(19/20) = (20/10) * 7/19 = 14/19.
Reply:P(at least 25 hours more] already lasted 40 hrs) = (.95-.7)/.95=26.3%