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Answer:
The percent of the parts are expected to fail before the 2100 hours is 0.15.
Step-by-step explanation:
Given :Life tests on a helicopter rotor bearing give a population mean value of 2500 hours and a population standard deviation of 135 hours.
To Find : If the specification requires that the bearing lasts at least 2100 hours, what percent of the parts are expected to fail before the 2100 hours?.
Solution:
We will use z score formula
Mean value =
Standard deviation =
We are supposed to find If the specification requires that the bearing lasts at least 2100 hours, what percent of the parts are expected to fail before the 2100 hours?
So we are supposed to find P(z<2100)
so, x = 2100
Substitute the values in the formula
Now to find P(z<2100) we will use z table
At z = −2.96 the value is 0.0015
So, In percent =
Hence The percent of the parts are expected to fail before the 2100 hours is 0.15.