Question

Thickness measurements of ancient prehistoric Native American pot shards discovered in a Hopi village are approximately normally distributed, with a mean of 5.4 millimeters (mm) and a standard deviation of 0.8 mm. For a randomly found shard, find the following probabilities.

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

a) the required probability is 0.0013

b) the required probability is 0.0288

c) the required probability is 0.9759

Explanation:

Given the data in the question;

let x be the thickness measurements

Given that X follows a Normal distribution with mean μ = 5.4

standard deviation σ = 0.8

then z = x-μ / σ = x-5.4 / 0.8 follows standard Normal

a) probability that the thickness is less than 3.0 mm

P( x<3 ) = P( x-5.4 / 0.8 < 3-5.4 / 0.8 ) = P( Z < -3.00 ) = 0.0013

Therefore, the required probability is 0.0013

b) the thickness is more than 7.0 mm

P( x>7 ) = P( x-5.4 / 0.8 > 7-5.4 / 0.8 ) = P( Z > 2.00)

= 1 - P( Z ≤ 2)

= 1 - 0.9772

= 0.0288

Therefore, the required probability is 0.0288

c) the thickness is between 3.0 mm and 7.0 mm

P(3< x<7 ) = P( x<7) - P(x<3)

= P( x-5.4 / 0.8 > 7-5.4 / 0.8 ) - P( x-5.4 / 0.8 < 3-5.4 / 0.8 )

= P( Z< 2 ) - P( Z < -3)

= 0.9772 - 0.0013

= 0.9759

Therefore, the required probability is 0.9759