# probability and percentile problem

#### Lucyzzz

For each probability and percentile problem, draw the picture.

Suppose that the useful life of a particular car battery, measured in months, decays with parameter 0.025. We are interested in the life of the battery.

Give the distribution of X.
X ~

I believe that is exponential distribution x ~Exp(1/0.025) but one question said Find the probability that a car battery lasts more than 38 months. (Round your answer to four decimal places.) I tried P(x equal or more 38) and use the formula e to the power of -mc an get zero. could someone tell me what I am doing wrong?

#### Walagaster

MHF Helper
For each probability and percentile problem, draw the picture.

Suppose that the useful life of a particular car battery, measured in months, decays with parameter 0.025. We are interested in the life of the battery.

Give the distribution of X.
X ~

I believe that is exponential distribution x ~Exp(1/0.025) but one question said Find the probability that a car battery lasts more than 38 months. (Round your answer to four decimal places.) I tried P(x equal or more 38) and use the formula e to the power of -mc an get zero. could someone tell me what I am doing wrong?
You haven't told us what form your exponential distribution formula uses. If its pdf is $\lambda e^{-\lambda x}$ you get the integral $\int_{38}^{\infty}.025 e^{-.025 x} dx= .3867$, which seems reasonable since the mean is $\mu = \frac 1 \lambda = 40$.

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#### Lucyzzz

Thank you so much that helped.