Question 353660
Find the z-score.
{{{z=(x-mu)/sigma}}}
{{{z=(10-7.8)/3=0.7333}}}
{{{P(z)=0.841345}}}
So then 
{{{P(x>10)=1-0.841345=0.158655}}}
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{{{z=(7.8-7.8)/3=0}}}
{{{P(z>7.8)=0.5}}}
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{{{P(z1)=0.01}}}
{{{z1=-2.57583}}}
{{{x1=-2.57583(3)+7.8}}}
{{{x1=0.072512}}} years