Math help needed ASAP please

**icemanfan** · February 18th 2010, 12:36 PM

Originally Posted by bathola

Can you show me the whole question completed so I can try to figure out how to do it? Thx.

Well, I would solve both questions with a table. Beyond what I have already told you, it basically boils down to being able to use the table correctly.

My table tells me that the probability of x being more than 1.35 standard deviations from the mean in the positive direction is 0.0885.

**bathola** · February 18th 2010, 12:45 PM

Originally Posted by icemanfan

Well, I would solve both questions with a table. Beyond what I have already told you, it basically boils down to being able to use the table correctly.

My table tells me that the probability of x being more than 1.35 standard deviations from the mean in the positive direction is 0.0885.

So 0.0885 is the answer. I don't understand how to put this all together. I don't even have those numbers on the table I am looking at. Can you write out how to do the problem with the formula right from the beginning. Sorry to be a pain, this is all foreign to me so to speak.

**icemanfan** · February 18th 2010, 12:56 PM

Originally Posted by bathola

So 0.0885 is the answer. I don't understand how to put this all together. I don't even have those numbers on the table I am looking at. Can you write out how to do the problem with the formula right from the beginning. Sorry to be a pain, this is all foreign to me so to speak.

Ok, so you want the probability that more than 300 meals are served given that the mean is 250 and the standard deviation is 37. The probability density function for the normal distribution is

$\frac{1}{\sigma \sqrt{2\pi}}\exp\left(-\frac{(x - \mu)^2}{2\sigma^2}\right)$ .

Therefore, the answer is

$\int _{300} ^{\infty} \frac{1}{37\sqrt{2\pi}}\exp\left(-\frac{(x - 250)^2}{2 \cdot 37^2}\right)dx$ .

Alternatively, you notice that 300 is 1.35 standard deviations away from 250 and use the table.

**bathola** · February 18th 2010, 01:06 PM

Originally Posted by icemanfan

Ok, so you want the probability that more than 300 meals are served given that the mean is 250 and the standard deviation is 37. The probability density function for the normal distribution is

$\frac{1}{\sigma \sqrt{2\pi}}\exp\left(-\frac{(x - \mu)^2}{2\sigma^2}\right)$ .

Therefore, the answer is

$\int _{300} ^{\infty} \frac{1}{37\sqrt{2\pi}}\exp\left(-\frac{(x - 250)^2}{2 \cdot 37^2}\right)dx$ .

Alternatively, you notice that 300 is 1.35 standard deviations away from 250 and use the table.

How do you put those math symbols on here. Can I work out everything you just gave me on a calculator, I am thinking that even though you put the anser is...I still need to calculate this?

**icemanfan** · February 18th 2010, 01:10 PM

Originally Posted by bathola

How do you put those math symbols on here. Can I work out everything you just gave me on a calculator, I am thinking that even though you put the anser is...I still need to calculate this?

You make the math symbols with LaTex. And I highly doubt that you were intended to calculate the answer to the question exactly by evaluating that integral of the probability density function.

**bathola** · February 18th 2010, 01:13 PM

Originally Posted by icemanfan

You make the math symbols with LaTex. And I highly doubt that you were intended to calculate the answer to the question exactly by evaluating that integral of the probability density function.

I appreciate you trying to help me. I'm not sure what you are telling me in that last sentence. Basically, you are talking to someone who knows nothing about statistics...absolutly nothing. I am so confused I can't grasp what you have been trying to show me at all. I could just cry.

**icemanfan** · February 18th 2010, 01:18 PM

Originally Posted by bathola

I appreciate you trying to help me. I'm not sure what you are telling me in that last sentence. Basically, you are talking to someone who knows nothing about statistics...absolutly nothing. I am so confused I can't grasp what you have been trying to show me at all. I could just cry.

In order to truly appreciate the value of the probability density function, you have to understand both calculus and probability. All I am saying is that there is an easy way to do the problem and a hard way to do it, and you should probably do it the easy way (seeing as you don't understand the hard way, and the easy way is just simpler).

**bathola** · February 18th 2010, 01:21 PM

Originally Posted by icemanfan

In order to truly appreciate the value of the probability density function, you have to understand both calculus and probability. All I am saying is that there is an easy way to do the problem and a hard way to do it, and you should probably do it the easy way (seeing as you don't understand the hard way, and the easy way is just simpler).

Lamen terms...this is good. I understood what you are telling me.

Problem is I don't even seem to grasp the easy way, and It doesn't look like I've been provided with a table that has the correct info on it.

**mr fantastic** · February 19th 2010, 01:24 AM

Originally Posted by bathola

Can anyone help me understand how to do these questions?

I f the number of meals served in a hospital is a normal distribution with amean of 250 and a standard deviation of 37

a) What is the probability that more than 300 meals are served?
B) For the middle 50% of the distribution, what is the range of the number of meals served?

Have you reviewed any examples from your class notes or textbook? Where are you stuck?

**ANDS!** · February 19th 2010, 07:01 AM

There is no way that your instructor is wanting you do know the normal distribution probability density function. That equation pops up in a "upper" lower division stats class, not a stats class for non math majors, which I am guessing this is.

Instead of beating your head against a wall using that equation, why not review your notes on normal distributions and calculating z-scores using a table and a TI83.

This problem should be done in a minute or so after consulting your notes on calculating z-scores (or finding z-scores when given a percentage):

Part A is very simply you plugging 300, 250 and 37 into the equation for a z-score. You should get 1.35. I will leave it to you to interpret the results (after consulting your notes).

Part B is remembering what you learned earlier in the semester about "quartiles" - and that the MIDDLE 50 percent corresponds to the 2 and 3 quartiles, i.e 25% to 75%. Therefore, using your z-chart (in your book, trust me you have one), locate the z-score that applies to .25 percent of the data under a normal curve, and .75 percent of the data under a normal curve. These will give you the z-scores. It is up to you to use the formula for computing a z-score to find the upper and lower bound.

No offense to the other poster, but do not make things more difficult than they are, and take Mr. F's advice and read your notes.

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