Math help please

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Sep 30, 2009 | 06:44 AM

#21

Red X

x pǝɹ

Joined: Feb 2003

Posts: 6,246

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From: Upstate

Quote:

Originally Posted by Line7

This is the other problem I need to solve, any insight on how to do it? Thanks for the help!

Monthly rainfalls in a tropical city are independents and normally distributed with an average of 60 cm and variance of 25 cm2, N(60,5). There is flood in the city if monthly rainfall exceeds 75 cm.
(a)What is the probability of having less than 50 cm?
(b)What is the probability of occurrence of flood?
(c)What is the probability that monthly rainfall exceeds 50 and no flood occurs?
(d)What will be the maximum monthly rainfall if probability of occurrence is 90%?

ok, this problem is relatively easy. I won't give solutions but I'll explain how to solve (I dont have the means or time to make calculations).

You first should graph what you have. You know its normally distributed, with a mean and a variance. Excel, Matlab, etc. can draw this graph for you.

a. the probability of having less than 50 is done by summing all the points from 50-inf and subtract that result from 1 (which is the area under the entire curve) and you'll get the probability for LESS than 50.

b. For a flood, you just sum from 75, inf and use that as the probability.

c. here you calculate probability from 50 to inf and subtract 75 to inf.

d. here you solve for when the probability is .9 (somewhere to the right of the mean)

Sep 30, 2009 | 06:46 AM

#22

Line7

Thread Starter

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Joined: Jun 2006

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From: cardboard box

I have no idea how you did that. Can you explain what formulas you used ?
Edit: N/M, Awesome, thanks guys.

Last edited by Line7; Sep 30, 2009 at 06:49 AM.

Sep 30, 2009 | 06:57 AM

#23

k3ifers

k three ifers

Joined: Jun 2002

Posts: 42,568

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From: Buffalo, NY

Quote:

Originally Posted by scotttharobot

i forgot how to do these almost instantly.

Sep 30, 2009 | 07:24 AM

#24

åhhhhh

Joined: Mar 2002

Posts: 7,992

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From: Toronto, Canada

wow.. for a second i thought i stepped into bizzarro basement.

Sep 30, 2009 | 07:42 AM

#25

shirley

CBOTY 2010

Joined: Nov 2004

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From: MI

Sep 30, 2009 | 08:02 AM

#26

cpvdh

Member

Joined: Feb 2006

Posts: 1,869

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From: OR

bwahahaha, if you are struggling with the math aspect now you are in for a rough term

Quote:

Originally Posted by LABARINTH

a) 0.02275
b) 0.00135
c) 1 - (0.02275 + 0.00135) = 0.9759 (between extremes a and b).
d) 66.408cm

I haven't taken statistics in 5 years so this could very well be wrong. I used a mean of 60cm, a standard deviation of 5cm (SQRT of 25cm2), and the fact that the data is normally distributed to solve these.

gf is applying at nsa for internship, fucking baltimore, why cant it be somewhere i can get a tan

Last edited by cpvdh; Sep 30, 2009 at 08:04 AM.

Sep 30, 2009 | 11:42 AM

#27

LABARINTH

Better Than Canada!

Joined: Dec 2002

Posts: 10,821

Likes: 0

From: Baltimore, MD

Help me solve this math problem.

Given the following.

196, 295, 394, 493, 592, Cheeseburger, 691

find Cheeseburger.

actually I know the answer I just wanted to see if anyone could solve it without google.

[SPOILER="answer"]689

h:[/SPOILER]