1 reply to this topic

[Fern]

I have found how to get either the probability or value of normally distributed data by entering the mean and standard deviation but I was wondering if there was any way to get the mean/ standard deviation from the probability and value for my S1 exam. Sorry I haven't explained very clearly.
Thank you in advance for your time and expertise.

[pan.gejt]

I assume you know the probability and mean or probability and standard deviation and the t-value is normalized.

You can choose from following methods:

 

1. spreadsheet calculations (brute force)

2. getting value from graph

3. getting value from handbook(s)

 

ad 1) this method consists in numerical calculations of probability based on t-value (Casio user's guide or x/u-value in hanbooks). Put the t-value in the first column, calculate the f(t) and use e.g. the trapezoidal rule to obtain the probability value. Compare the probability, find the proper t-value. By knowing t-value and mean or t-value and standard deviation you can calculate the non-normalized value (see the casio user's guide)

ad3) see the user's guide, page 6-20. You need to enter t-value only

ad3) You find the probability in the hanbooks and read the corresponding t-value. The following calculations is the same as in method 1.

 

Edited: You can use the built-in solver. Go to EQUA menu, press F3 (Solver) and input the equation

A=1/sqrt(2pi)*int(e^-(X^2/2),0,T) and press enter. 

 

A- the probability value

X- variable

T- t-value

sqrt - square root symbol (shift + x^2)

int - integration symbol, available via optn-calc

fill the probabilty value to A, leave the X as 0 and put the cursor on T and press F6 (solv). This settings corresponds to Q(t)

 

But remember, the A must be from interval (0;0.5).

 

With same procedure you can calculate mean or standard deviation. Just type the equation, fill the known values and solve the equation.

Edited by pan.gejt, 03 March 2015 - 07:19 AM.