<PRE><B>Question 969359</B>
With 2 SDs, it would be 9.1 days, and 97.1% working is very close to 97.5%, so I would expect the number to be close to 9.1 days, but a littleness.

Using a z-table or a calculator, 0.971 on the z-table (0.029) is with a z-score of 1.895 (at 1.89, the z-score is 0.9706 and at 1.90 it is 0.9713).  

z=(Value-mean)/SD
1.895=Value-4.3/2.4   Multiply by 2.4
4.548=Value-4.3         Add 4.3
8.848=Value or 8.8 days.

Check
(8.8-4.3)/2.4 = z= (4.5/2.4)=1.875.  This rounds to 0.970.
(8.9-4.3)/2.4=z=1.917  This rounds to 0.972.  
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