Question

Are my answers right?
The trees in a cutting block have an average diameter of 35 cm, have a standard deviation of 6 cm and are normally distributed.
a. proportion of trees is less than 25 cm in diameter ?
b. proportion of trees is greater than or equal to 25 cm and less than or equal to 40 cm?
c. proportion of trees is greater than 40 cm?

A) P(X<25)
=P(Z<(25-35)/6
=P(Z< -1.67)
.0475

B) P(25≤X≤40)
=P(X≤40) - P(X≤25)
=P(Z≤ (40-35)/6 ) - P(Z≤ (25-35)/6 )
=P( Z≤ .833) - P(Z≤ 1.67)
=.7967-.0475
=.7492

C) P(X>40)
=P(Z>(40-35)/6
=P(Z>.833)
= 1.0 - .7967
= .2033

Answer 1

Looks right to me.