MTTFS
The quantity MTTF ( ) can be obtained from equation (4.8a) using the relationship expressed in System MTTF and Failure Rates with No Maintenance, i.e.:
which, because μ>>λ, can to a good approximation, be written in the form:
However, if μ=0, equation (4.9a) becomes 
, a fundamental result.
, a fundamental result. | This result can also be obtained by integrating the right-hand side of equation 2.10 fromt=0 to t=∞ and letting λA=λB=λ. |