If one assumes
that other star systems, with non sunlike stars, have the
same or similar planetary frequency, then equation 7.1.1
can be modified in such a way that it applies to any star
quantity N_{X}:
7.2.1 Equation 
N_{X}
= A·F_{X} 
F_{X} is the probability for the occurrence of a set
of stars that have a certain property, namely the spectral class.
A = 200 – 300 billion is
the number of stars
in the galaxy.
This concept can be applied to all stars for which
observational data are available .
Looking at the planets, an equation for the probability
of a habitable planet, in any system, can be set up:
7.2.2 Definition 
F_{ph}
= F_{p}·F_{h} 
F_{ph} = 201:14,000 · 10:603 = 1:4,200
Among 4,200 star systems is one that possesses planets
and among them at least one habitable planet exists.
Then for the set of all systems N_{phx} of a spectral class with
planets and at least one in the habitable zone:
7.2.3 Equation 
N_{phx}
= A·F_{X}·F_{ph}
= A·F_{X}·F_{p}·F_{h} 
For the set of all solar systems N_{phxGal} in the galaxy, with planets
and at least one in the habitable zone:
7.2.4 Equation 
N_{phxGal}
= ∑ N_{phx} 

The following applies:
N_{phxGal}
= ∑ N_{phx} = ∑ (A·F_{X}·F_{p}·F_{h})
Since A remains the same
for all spectral classes, A can be drawn from the sum:
N_{phxGal}
= ∑ N_{phx} = A·∑ (F_{X}·F_{p}·F_{h})
Under
a first assumption that F_{p} and F_{h} remain the same
for all spectral classes, they can also be drawn from the
sum:
N_{phxGal}
= ∑ N_{phx} ≈ A·F_{p}·F_{h}·∑
(F_{X})
The
sum over all spectral classes (for the probabilities F_{X}) yields the
entirety of the stars in the galaxy, so:
∑
(F_{X})
= 1
It is thus a
total of:
7.2.5 Equation 
N_{phxGal}
= ∑ N_{phx}
≈ A·F_{ph} 

7.2.6 Theorem 
The amount of all star
systems, in the galaxy, with planets and at least
one in the habitable zone, is 47.619 to 71.428
million. 
It is important here that all factors can be determined
empirically by appropriate instruments of observation.
