Math Is Fun Forum

lovely lady 74

Member

Registered: 2010-01-06

Posts: 2

Older woman back in school, can not figure out Math probability.

The xyz company tested a new product and founds its lifetime to be normally distributed, with a mean life of 146 days and a standard deviation of 19.5 days. What is the probability that a product selected at random will last longer than 166 days?

The answer I can up with is 0.3485 is this correct?

Also for the same company what is the probability that the product will last between 154 and 180 days?

The answer I came with is 0.200 is this correct?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Older woman back in school, can not figure out Math probability.

Hi lovely lady 74;

The answer I can up with is 0.3485 is this correct?

This answer is not correct. Please show what you have done and I will correct your error. Your work here is important for me to show the exact reason why you are in error and get you to understand the correct way. Please provide what you have.

The answer I came with is 0.200 is this correct?

You made the exact same mistake here. It is an error in understanding, please allow me to fix it by showing me what you have done.

Take heart your method is fine, you just aren't looking at it right.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

lovely lady 74

Member

Registered: 2010-01-06

Posts: 2

Re: Older woman back in school, can not figure out Math probability.

I am at work right now.  I don't have what I did with me.  All i can remember is that I created some sort of graph and tried some formulas in the text.  I keep getting the same answers.

I had asked someone here to take a look and they came up with 0.1515 for the first part and 0.8485 for the second.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Older woman back in school, can not figure out Math probability.

Hi lovely lady 74;

Your answers are correct except you are measuring the wrong part of the SNC.

.5 - 0.3485 = .1515 Close! Your friend is close too! Actually the exact answer is closer to .1525, but could be an error in the table.

.5 - .200 = .3 Correct ! Your friend is not right!

Come back when you have some time and show your steps and I will try tp show you how not to make this mistake again.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Sarah Rebekah 13

Guest

Re: Older woman back in school, can not figure out Math probability.

Hi Lovely Lady Are You 74?