Question
A sample of concrete specimens of a certain type is selected, and the compressive strength of...
A sample of concrete specimens of a certain type is selected, and the compressive strength of each specimen is determined. The mean and standard deviation are calculated as x = 4000 and s = 300, and the sample histogram is found to be well approximated by a normal curve.
(a)Approximately what percentage of the sample observations are
between 3700 and 4300? (Round the answer to the nearest whole
number.)
Approximately %
(b) Approximately what percentage of sample observations are
outside the interval from 3400 to 4600? (Round the answer to the
nearest whole number.)
Approximately %
(c) What can be said about the approximate percentage of
observations between 3400 and 3700? (Round the answer to the
nearest whole number.)
Approximately %
Homework Answers
Answer #1
(a)
P[3700 <X<4300]
=P[-1<Z<1]
=0.8413-0.1587.....................by using normal probability table.
=0.6826
Therefore, 68 %of the sample observations are between 3700 and 4300
(b)
1-P[3400 <X<4600]
=1-P[-2<Z<2]
=1-{0.9772-0.0228}................by using normal probability table.
=0.0456
Approximately 5%
(c) P[3400 <X< 3700]
=P[-2<Z<-1]
=0.1587-0.0228...........................by using normal probability table.
=0.1359
Approximately 14 %
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