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: a customer bought a product at the shop . however , the shopkeeper increased the price of the product by 10 % so that the customer could not buy the required amount of the product . the customer managed to buy only 80 % of the required amount . what is the difference in the amount of money that the customer paid for the second purchase compared to the first purchase ? 
Options: a ) 10 % , b ) 12 % , c ) 14 % , d ) 16 % , e ) 18 %
[EX A]: b

[EX Q]: Problem: how many times digit 5 is used while writing numbers from 100 to 1000 ? 
Options: a ) 648 , b ) 300 , c ) 252 , d ) 225 , e ) 290
[EX A]: e

[EX Q]: Problem: the average of first thirteen prime numbers which are odd is ? 
Options: a ) 20.15 , b ) 21.15 , c ) 22.15 , d ) 23.15 , e ) 24.15
[EX A]:
b