theory - Current divider rule calculation issue

I'm doing the exercises from Wisc-Online. This one

I think they are really great to learn and practice and have already done a bunch of their practical trainings. But here I'm starting to be crazy. I need to calculate \$I_{r1}\$

Here's the schema :

^{simulate this circuit – Schematic created using CircuitLab}

According to their lesson :

\$I_{Rx} = \dfrac{R_{T}}{R_{x}} \times I_{T}\$

So :

\$I_{R1} = \dfrac{R_{1} \parallel R_{2}}{R_{1}} \times I_{T}\$

With values :

\$I_{R1} = \dfrac{\dfrac{1}{\cfrac{1}{5000}+\cfrac{1}{10000}}}{\dfrac{1}{5000}} \times 3mA\$

\$I_{R1} = 50000mA\$

But the answer should be 2mA

What's wrong in my formula ? :'(

Answer

Sorry... I just figured out what was wrong... It's not :

\$I_{R1} = \dfrac{\dfrac{1}{\cfrac{1}{5000}+\cfrac{1}{10000}}}{\dfrac{1}{5000}} \times 3mA\$

But :

\$I_{R1} = \dfrac{\dfrac{1}{\cfrac{1}{5000}+\cfrac{1}{10000}}}{5000} \times 3mA\$

And in that case I've got the correct answer.

Sorry.