Question

A manufacturer of personal computers sets tests competing brands and finds that the amounts of energy they require are normally distributed with a mean of 285 kwh and a standard deviation of 9.1 kwh.
If the lowest 25% are not included in a second round of tests, what is the lower limit for the energy amount of the remaining set? Give your answer to 4 decimal places.

A manufacturer of personal computers sets tests competing brands and finds that the amounts of energy they require are normally distributed with a mean of 285 kwh and a standard deviation of 9.1 kwh.
If the highest 30% are not included in a second round of tests, what is the upper limit for the energy amount of the remaining set? Give your answer to 4 decimal places.

Answer 1

(there are more than 1 different questions, as per policy i am answering first question)

question 1 :

P(z<Z) table :

for lowest 25% :

P(x<X) = 0.25

P(z<Z) = 0.25

from table : Z = -0.67

X = mean + Z*SD

= 285 - 0.67*9.1

= 278.903 KWh

278.903 KWh is the lower limit for the energy amount of the remaining set

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