Am I doing it right?

[gasoltub]

Disclaimer: I have used the search function. But perhaps this is too simple to be mentioned here. And yes, I'm new at this.

Anyway...

I'm learning about calculating odds so I thought I'd post one here just to verify that I'm doing it right.

The odds in question is backdoor flush draw. Lets say I have pocket hearts and flop is one heart and two other. What's the odds of making a flush by the river?

After the flop there are 47 cards left in the deck and 10 of them are hearts. That gives me about 21% chance to hit a heart on the turn.
If hit a heart on the turn there are 46 cards left in the deck and 9 of them are hearts. That means about 20% to get a heart on the river.

So I would have 0.21*0.2 = 4.2% chance to get a flush by the river. The reciprocal of 4.2% is roughly 24. So I would get my flush once every 24 times. Which makes me a 23:1 dog.

Correct?