Answer:
2800
Step-by-step explanation:
The choice at any node (except the edges) is to go right or go down.
A to B
To get from A to B requires a total of 4 choices to go down, and 4 choices to go right. Those can occur in any order. Locating the "right" choices in the list of "all" choices is effectively choosing 4 of 8. The number of ways those choices can be made is ...
C(8, 4) = 8!/(4!(8-4)!) = 8·7·6·5/(4·3·2) = 70
B to C
Similarly a total of 2 choices must be made, 1 of which is a "right" choice. The number of ways those can be ordered is ...
C(2, 1) = 2 . . . . . . . that is: (right, down) or (down, right)
C to D
A total of 6 choices must be made, of which 3 are "right." The number of possible orderings is ...
C(6, 3) = 6·5·4/(3·2·1) = 20
Total paths
Each set of choices is independent of the others, so the total possible number is the product of the numbers of choices on the subpaths:
total paths = (70)(2)(20) = 2800
There are 2800 possible paths from A to D.
