Here is the question:
For a tire manufacturing company, it is known that only 7% of their tire
products last less than 35 months, whereas 11% of them last more tham 63
months. Assuming the distribution of the lifetime of the manufactured tires
(a) what is the expected lifetime for a tire manufactured by this company,
and its standard deviation?
(b) The manufacturer company gives a warranty that if the tire does not last
more than 40 months, they will give a replacement for it. The company
sold 1000 tires during the last year. What is the probability that they
will have to replace more than 50 tires?
So I have
a) P (X <= 35 months) = 0.07
P (X >= 63 months) = 0.11
and for b I've started with...
b) P ( X <= 40 months) = ...?
Where do I go from here, for each part?
Thank you so much in advance : )