#### Answer

24

#### Work Step by Step

The number of ways in which a series of successive things can occur is found by multiplying the number of ways in which each thing can occur.
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1. The path from A to B can be chosen in 3 ways.
2. The path from B to C can be chosen in 2 ways.
3. The path from C to D can be chosen in 4 ways.
Applying the Principle,
the total number of routes from A to D is 3$\times$2$\times$4$=24$