Normally distributed student reaction time

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Homework Statement

In a lab, the reaction time of the students to an event related to the experiment they are conducting is normally distributed with $\mu=0.5$ seconds, and $\sigma=0.05$ seconds.
1) What is the probability that a student will react after more than $0.5$ seconds?
2) What is the probability that a student's reaction time falls between $0.45$, and $0.55$ seconds?
3) What is the reaction time that is exceeded $90\%$ of time?

Relevant Equations

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1) $P(X>0.5)=P(Z>0)=0.5$
2) $P(0.45<X<0.55)=P(X<0.55)-P(X<0.45)=P(Z<1)-P(Z<-1)\approx68\%$
3) $P(X>x)=0.9\Leftrightarrow P(Z>\frac{x-0.5}{0.05})=0.9\Leftrightarrow1-P(Z\leq\frac{x-0.5}{0.05})=0.9\Leftrightarrow P(Z\leq\frac{x-0.5}{0.05})=0.1$
I find that $\frac{x-0.5}{0.05}=-1.28$, which gives me $x=0.436$.

Correct? Thank you!

 

[mfb]

Looks fine.