HP 39gs Master Manual page 306

(ii) Predict N for t = 15 hours.
In the view, press up arrow to move the cursor onto the
PLOT
curve of best fit. Now press
cursor will jump to the predicted value for x=15, which is
currently off screen.
Alternatively, change to the
function.
Result: 268 269 colonies.
N =
(iii) Find t so that
Step 1. Find the values of
and k into memory K, so that it is un-necessary to re-type them.
See page 135 for instructions on finding the parameters from
the exponential fit curve.
Step 2. Switch to the Solve aplet and enter the equation to be solved.
Changing into the
and already defined, so move the highlight to
K
.
Result: Doubling time is 1.0536 hours.
and enter the value 15. The
view and use the
HOME
1
.
N
0
2
and k and store
N N
0
view, you should find the values of
NUM
PREDY
into memory A
0
A
and press
T
306