HP 39gs Master Manual page 103

Population type problems are also easily dealt with in this way.
For example, "A population of mice numbers 5600 and is growing at a rate of 12.5% per
month. How long will it be until it numbers more than one million?"
Pressing (above
CLEAR
we can enter the formula for the GP modeling the situation shown right.
Because this is a non-recursive rule, the two initial values of 5600 and
6300 will be automatically calculated when you enter the rule into
.
U1(N)
All we need do now is switch to the Numeric view to find, with some
experimenting, that
U1(46)
It is also possible to answer these questions in the Solve aplet. For
example if we use the Sequence aplet to define
before, then we can change to the Solve aplet and enter into
equation
U1(N)=10000
and obtain an answer of 14 29 . This means, of course that
the first term exceeding 10000.
The reason why we did not use
though no error message is given if you try.
) clears out the existing expressions, and
DEL
is the first to exceed one million.
, change to the NUM view and press
⋅
is that the Solve aplet is unable to deal with inequalities even
E1(N)>10000
as
U1(N)=2^(N-1)
the
E1
is
N=15
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