Question

Suppose the height of an 18 year old boy is normally distributed with mean 187cm fifteen percent of 18 year old boys have heights greater than 193cm. Find the probability that two 18 year old boys chosen at random will have heights greter than 185cm

Answer 1

the probability that two 18 year old boys chosen at random will have heights greater than 185cm is 0.403

Explanation:

P( x > 193) = 0.15

= 1- p(x less than or equal 193)

= 1 -p( z < (x- u) /sigma)

= 1- p( z< (193 - 187)/ sigma)

= 1- p( z< 6/ sigma)

P(z< 6/sigma) = 1 - 0.15

P(z < 6/sigma)= 0.85

6/sigma =1.036

Sigma= 6/1.036

Sigma= 5.79

P( x> 185) = 1- p( x< 185)

= 1- p (z < (185- 187)/5.79)

= 1- p( z< -0.345)

= 1- 0.365

= 0.635

P (x> 185) = 0.635 × 0.635

=0.403