
105Chapter ve: The fundamental solution for reliability assurance:
Let’s consider the meaning of the two equations for sample size,
Equations 5.9 and 5.11. Multiplying the numerator and denominator of
Equation (5.11) by the lifetime or target period (L
*
) yields
n r
L
L
AF h
r
x
L
AF h
a a
≥ +
( )
⋅
⋅
⋅
⋅
= +
( )
⋅ ⋅
⋅
1
1
1
1
λ
* *
* *
1
(5.12)
Here, λ
*
· L
*
becomes the cumulative failure rate (x), as it is the result of mul-
tiplying the failure rate per period by the specied period (for example,
lifetime).
Comparing the sample size equations for failure rate (Equation (5.12))
and for lifetime (Equation (5.9)) implies that they have a similar form. The
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