HP 39g Master Manual page 292

(ii) Predict N for t = 15 hours.
Change to the HOME view and use the PREDY
function.
Result: 268 269 colonies.
(iii) Find t so that
Step 1. Find the values of
into memory A and k into memory
N
0
K, so that it is un-necessary to re-type
them.
See page 145 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 NUM view, you should find the
values of A and K already defined, so
move the highlight to T and press
.
Result: Doubling time is 1.0536 hours.
1
=
.
N N
0
2
and k and store
N
0
292