T
he time
that
a laptop battery lasts in everyday use before recharge is needed
is normally
distributed, with a mean of 270 minutes
and
a standard deviation o
f 55 minutes.
a) What is the probability that the battery lasts
more than four hours?
b) What value of
battery
life in minutes is exceeded with 95 % probability?
c) What is the probability
that
the battery lasts exactly
300 minutes?
Let "X=" the time of a laptop battery: "X\\sim N(\\mu, \\sigma^2 )."
Given "\\mu=270min, \\sigma=55min."
a)
"\\approx1-P(Z\\le-0.54545)\\approx0.70728"
b)
"\\dfrac{x-270}{55}=-1.6449"
"x=270-55(1.6449)"
"x=179.53\\ min"
c)
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