Question

Thickness measurements of ancient prehistoric Native American pot shards discovered in a Hopi village are approximately normally distributed, with a mean of 5.5 millimeters (mm) and a standard deviation of 1.5 mm. For a randomly found shard, find the following probabilities. (Round your answers to four decimal places.) (a) the thickness is less than 3.0 mm (b) the thickness is more than 7.0 mm (c) the thickness is between 3.0 mm and 7.0 mm

Answer 1

Solution :

Given that,

mean = = 5.5

standard deviation = = 1.5

a ) P( x < 3.0 )

P ( x - / ) < ( 3.0- 5.5 / 1.5)

P ( z < -2.5 / 1.5 )

P ( z < -1.67)

= 0.0475

Probability = 0.0475

b ) P (x > 7.0 )

= 1 - P (x < 7.0)

= 1 - P ( x -  / ) < ( 7.0 - 5.5 / 1.5)

= 1 - P ( z <2.5 / 1.5 )

= 1 - P ( z < 1.67)

Using z table

= 1 - 0.9525

= 0.0475

Probability = 0.0475

c ) P (3.0 < x < 7.0 )

P (3.0 - 5.5 /1.5) < ( x -  / ) < ( 7.0 - 5.5 / 1.5)

P ( - 2.5 / 1.5 < z < - 7 / 1.5 )

P ( -1.67 < z <1.67)

P ( z < 1.67 ) - P ( z < -1.67)

Using z table

= 0.9525 - 0.0475

= 0.9050

Probability = 0.9050