CAT 1991 QA Question 18 · Modern Math - Permutation & Combination

To go from A to B, we need to pass through 3 levels of nodes.

Number of ways of goind from A to any of the level 1 node = 4
Number of ways of goind from any of the level 1 node to any of the level 2 node = 2
Number of ways of goind from any of the level 2 node to B = 2

Total number of ways to reach A to B = 4 × 2 × 2 × 1 = 16.

Hence, option (b).