Question

onuts have weight taht are normally distributed with a mean 80 grams and standard deviation of 6 grams . they sold in packeages containing 12 randomly selected donuts.
a) what percentage of the donuts wiegh more than 75 grams ?
b)what is the probablity that the total weigh of the donuts package is less than 900 grams?

Answer 1

Solution :

Given that,

mean = =  80

standard deviation = = 6

n=12

= = 80

= / n = 6 / 12 = 1.7305

P( > 75 ) = 1 - P( < 75)

= 1 - P[( - ) / < (  75-80) /1.7305 ]

= 1 - P(z < -2.89)

Using z table

= 1 - 0.0019

= 0.9981

answer=99.81%

(B)

P( <900 ) = P[( - ) / <( 900-80) /1.7305 ]

= P(z < 473.85)

Using z table  

=1

probability=1