What is the probability a random journey from A to B passes through the point D? You can only move right or up.

I got 10 ways from A to D and 5 ways from D to B. I also got 210 ways from A to B.

Then $\displaystyle Pr(Passes through D)=\frac{10\cdot 5}{210}=\frac{5}{21}$

The anwers give $\displaystyle \frac{1}{21}$ please help with what I did wrong!