How many paths are there from C to D, if we can only move right or down and must stay on the grid? (Its not 220.)
Look at this video.
By using the water flow method.
We get a final answer of 126 + 84 = lolololol
We have the set ...... ( R, R , R ,R, D, D, D , D , D , D)
We can choose any 4 of 10 positions in the set to place the R or 6 of 10 postions in the set to place the D
We can either use C(10, 4) or C(10,6) = 210 paths