Answer:
a) the probability that the strength of a sample is less than 38 lb/in² is approximately 0.9332
b) approximately 0.62% of the sample are scrapped
Step-by-step explanation:
a)
What is the probability that the strength of a sample is less than 38 lb/in²?
lets X rep the paper tensile strength in pounds per square inch.
the probability that the strength of the sample is less than 38 lb/in²
i.e P( X < 38 )
so assuming that X is normally distributed with u = 35 lb/in² and α = 2 lb/in²,
so the probability expression P( X < 38 ) can be standardized as
P( X < 38 ) = P( (X-35)/2 < (38-35)/2)
= P( X < 1.5 )
from the cumulative standard normal distribution table,
we find P( X < 1.5 ) = 0.9332
so
P( X < 38 ) = P( X < 1.5 )
= 0.9332
therefore the probability that the strength of a sample is less than 38 lb/in² is approximately 0.9332
b)
If the specifications require the tensile strength to exceed 30 lb/in², what proportion of the samples is scrapped?
this can be represented as P( X < 30 )
By standardization the probability expression P( X < 30 ) can be transformed as;
P( X < 30 ) = P( (X-35)/2 < (30-35)/2)
= P( z < -2.5 )
from the cumulative standard normal distribution table,
we find P( X < -2.5 ) = 0.0062
so
P( X < 30 ) = P( X < -2.5 )
= 0.0062
therefore, approximately 0.62% of the sample are scrapped
