Say, I have unfair coin. When I toss it, probability of a head is 0.1, and probability of a tail is 0.9.

I toss this coin 10 times. What is the probability I get 7 heads and 3 tails?

I tried to draw a tree, but after 10 levels I gonna have 1024 branchs. My calculator has Pr and Cr functions, but I don't even know it's a Pr or Cr problem.

Sorry I'm not a good math people.