In this task, you need to provide the correct option for a given problem on probability from the provided options.

Example Input: Problem: how many positive integers less than 600 can be formed using the numbers 1 , 2 , 3 , 5 and 6 for the digits ? 
Options: a ) 48 , b ) 130 , c ) 66 , d ) 68 , e ) 84
Example Output: b

Example Input: Problem: if a coin is flipped , the probability that the coin will land heads is 1 / 2 . if the coin is flipped 6 times , what is the probability that it will land heads up on all 6 flips ? 
Options: a ) 1 / 6 , b ) 1 / 8 , c ) 1 / 32 , d ) 1 / 2 , e ) 1 / 64
Example Output: e

Example Input: Problem: a fair coin is tossed 4 times . what is the probability of getting at least 2 tails ? 
Options: a ) 1 / 16 , b ) 1 / 2 , c ) 3 / 16 , d ) 11 / 16 , e ) 3 / 8
Example Output:
d