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'.

Problem: if xy > 0 , 1 / x + 1 / y = 4 , and 1 / xy = 6 , then ( x + y ) / 2 = ? 
Options: a ) 1 / 25 , b ) 1 / 6 , c ) 1 / 5 , d ) 1 / 3 , e ) 6
d

Problem: a sum of money lent out at s . i . amounts to a total of $ 480 after 2 years and to $ 680 after a further period of 5 years . what was the initial sum of money that was invested ? 
Options: a ) $ 360 , b ) $ 380 , c ) $ 400 , d ) $ 420 , e ) $ 440
c

Problem: if 25 % of a number is equal to one - third of another number , what is the ratio of first number to the second number ? 
Options: a ) 4 : 3 , b ) 1 : 4 , c ) 3 : 7 , d ) 6 : 11 , e ) 2 : 3

a