Normal distribution - avoid negative

[royend]

Hi.
I have tried different tools and addons for excel but I am having
trouble creating a normal distribution without a negative x-axiz.

Example:
I want to present a normal distribution for a quiz for students,
testing how long they need to solve a mathematical problem. The time
varies from 0 to 300 seconds, and most students answer within 10
seconds, some even at once (like you would have done when the question
is 2+2?).

When I make this with PHStat, XLStat, PlotManager or by using Excel's
tools, I always end up with an x-axis that goes from -something to
+something. What I need is the normal distribution to be represented
within 0 to 300 seconds.

Can you help me?

Mean of my data is 35.
Standard deviation is 45 (as some answer very late...)

Thanks in advance.
royend

 

[Guest]

You don't need a normal distribution.


The normal distribution has an infinitely long tail. Even though the mean
may be very far from zero and the standard deviation may be very small, The
possibility for negative values still exists. Pick a different distribution.
See:

http://www.itl.nist.gov/div898/handbook/eda/section3/eda366.htm

 

[Stan Brown]

I have tried different tools and addons for excel but I am having
trouble creating a normal distribution without a negative x-axiz.

Can you help me?

Mean of my data is 35.
Standard deviation is 45 (as some answer very late...)

If the mean is 35 and the standard deviation is 45, then the normal
distribution will have 22% of all the data below zero. If the data
are intrinsically non-negative, then a normal distribution is not
just wrong for your data, it's very wrong.

Ask over in sci.stat.edu and they'll help you figure out what you
actually need to do, statistically. *Then* you can worry about how to
do it in Excel.