Answer
$α_c=0.01021$
Work Step by Step
$1-α=(1-α_c)^k$. Let's solve for $a_c$:
$\sqrt[k] {(1-α)}=1-α_c$
$α_c=1-\sqrt[k] {(1-α)}$
For $k=5$ and $α=0.05$
$α_c=1-\sqrt[5] {(1-0.05)}$
$α_c=0.01021$
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