Question

The heights of trees in a certain park are normally distributed with a mean of 30 feet and a standard deviation of 4 feet. What percentage of the trees are between 28 and 36 feet tall? Round the answer to the nearest hundredth.

Answer 1

P ( 28 < x < 36 )
(28 - 30 ) / 4 = -1/2
( 36 - 20 )/ 4 = 4
=> P ( -.5 < z < 4 )

Answer 2

Can you look up Z score table now?

Answer 3

do I look up the Z table for -.5 and 0?

Answer 4

-.5 and 4

Answer 5

like -.5 and .04?

Answer 6

Oops (36 - 30)/ 4 = 1.5

Answer 7

Just look up Z = .5 and Z = 1.5

Answer 8

okay so look up the z table for 1.5?

Answer 9

okay

Answer 10

Yep!

Answer 11

Then P ( 1.5 ) - P ( .5 ) =

Answer 12

.9332

Answer 13

do I X that by 30 (the mean)

Answer 14

What do you mean?

Answer 15

ohh so .9332 is the answer? I meant is there a next step after finding the Z score?

Answer 16

because the question is asking for a percentage, so I didn't know what to do after i found the z score again.

Answer 17

z score is .5 and 1.5
You look up from z score to find percent P!

Answer 18

Then subtract to find the middle!

Answer 19

so the percent would be 93.32% ?

Answer 20

Did you subtract P(1.5 ) - P(-.5) ?

Answer 21

ohhhhhh...I get it now, no. HOld on!

Answer 22

it equals .2417

Answer 23

so does that turn into the percent?

Answer 24

Finally, I can relax to hear "Ohhhh.... " :P

Answer 25

The table you look it up IS Percentage, Sir!

Answer 26

haha! not unless I don't pass the test! i have to do it over again. just 3 more days until I graduate so, It's worth it if i have to stay up all night.lol but i'll find someone else to pester with my math questions.

Answer 27

you mean M'am!

Answer 28

Ohh, I see ;)

Answer 29

PASSED! thank you!

Answer 30

How do you know PASSED?

Answer 31

Don't forget to round the result to nearest hundreth, though!