Question 7
A treasure chest is on the island shown.
The beaver receives a six-step route. Each step moves exactly 1 km south (N, the Vietnamese abbreviation for Nam) or east (Đ). The route must avoid the shark-filled sea. How many such instruction strings lead to the chest? For example, NĐĐĐNN is valid. Compass labels are north at top, south at bottom, west left and east right.
The beaver receives a six-step route. Each step moves exactly 1 km south (N, the Vietnamese abbreviation for Nam) or east (Đ). The route must avoid the shark-filled sea. How many such instruction strings lead to the chest? For example, NĐĐĐNN is valid. Compass labels are north at top, south at bottom, west left and east right.