Hi math,

There are a number of syntax errors you will find corrected below. (Look up FindFit in the help system!)

Best, David

In[1]:= xData = {19.38, 39.36, 58.62, 78.6, 99, 119.4, 138.6, 158.4, 
  199.2, 219, 239.4, 259.8, 278.4, 299.4}; yData = {23.1667, 59.1667, 
  147, 176.667, 228.333, 266.667, 300, 330, 401.667, 413.333, 425, 
  415, 408.333, 446.667};

In[2]:= (* FindFit wants pairs *)
data = Transpose@{xData, yData};

In[3]:= (* the model is an expression for the dependent variable in \
terms of the independent and parameters. Note the space in b x, and \
also the curly braces for lists *)
solution = FindFit[data, (a/b)*(1 - E^(-b x)), {a, b}, x]

Out[3]= {a -> 2.91944, b -> 0.00494724}

In[4]:= Show[ListPlot[data, PlotStyle -> Red], 
 Plot[(a/b)*(1 - E^(-b x)) /. solution, {x, 19, 450}]]

Attachments:

Hi David, Thanks for the help.

y=a/b(1-exp(-bx))

x={19.38, 39.36, 58.62, 78.6, 99, 119.4, 138.6, 158.4, 199.2, 219, \ 239.4, 259.8, 278.4, 299.4}; y={23.1667, 59.1667, 147, 176.667, 228.333, 266.667, 300, 330, 401.667, 413.333, 425, 415, 408.333, 446.667}

Need to find a and b.

I tried Findfit, but in vain.

When I take the ratio of 2 x and 2 y's, I get the following equation to solve -36 - 23.1e^(-39.36 b) + 59.1e^(-19.38 b) == 0, b but Solve was unable to solve the system with inexact coefficients or the \ system obtained by direct rationalization of inexact numbers present \ in the system. Since many of the methods used by Solve require exact \ input, providing Solve with an exact version of the system may help.