You didn't do anything wrong. 0.0181 is correct.
Calculating a poisson probability one uses the formula (at least at this point in my class)
e^(-y) times (y^x)/(x!)
where x is the number of occurrences and y is the average number of occurrences per time period.
for x=10 and y=5 I get
e^(-5)*((5^10)/(10!))
e^(-5) = 0.00673794699
5^10 = 9765625
10! = 3628800
so we have 0.00673794699 times (9765625/3628800)
becomes 0.00673794699 times 2.69114445547
which gives 0.01813278868 or 0.0181 to four decimal places
But the correct answer is supposed to be 0.0137
where did I go wrong?