2002 AMC 12B Question 22

For all integers $n$ greater than $1,$ define $$
a_n=\dfrac{1}{\log_n 2002}.
$$ Let $b=a_2+a_3+a_4+a_5$ and $c=a_{10}+a_{11}+a_{12}+a_{13}+a_{14}.$ Then $b-c$ equals