Problem of the Day


The GMAT Math Pro logo is stuck on the highest ledge of a nine-story building and must climb down to the single ledge on the bottom row to get to safety. Each move he makes must be to a ledge on the level immediately below him and to the immediate right or left of the ledge on which he’s currently standing. If all available ledges are pictured in the above diagram, how many paths can he take to get to safety?

A. 18
B. 70
C. 128
D. 256
E. 512

Reveal Answer

Answer

B. 70

See the Solution

Solution

For any given ledge, the number of ways he can get there is equal to the sum of the ways he can get to the ledges immediately above him. So, start at the top ledge with the number 1, and fill in the number of ways to get to each ledge. It should look like this:

 

So, there are 70 ways to get to the bottom ledge.

 

 

 

 

 

 

 

 

 

 

 

 

 


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