In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: how many odd 3 - digit integers greater than 800 are there such that all their digits are different ? 
Options: a ) 40 , b ) 56 , c ) 72 , d ) 81 , e ) 104
[EX A]: c

[EX Q]: Problem: a rower whose speed is 2.5 km / hr in still water rows to a certain point upstream and back to the starting point in a river which flows at 0.5 km / hr . what is the rower ' s average speed ( in km / hr ) for the total journey ? 
Options: a ) 2.2 , b ) 2.3 , c ) 2.4 , d ) 2.5 , e ) 2.6
[EX A]: c

[EX Q]: Problem: the sum of first n consecutive odd integers is n ^ 2 . what is the sum of all odd integers between 15 and 41 inclusive . 
Options: a ) 351 , b ) 392 , c ) 410 , d ) 424 , e ) 450
[EX A]:
b