In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: to produce an annual income of rs . 800 from a 8 % stock at 90 , what is the amount of stock needed ? 
Options: a ) 10000 , b ) 11000 , c ) 12000 , d ) 13000 , e ) 14000
[EX A]: a

[EX Q]: Problem: in how many years will a sum of money doubles itself at 12 % per annum on simple interest ? 
Options: a ) 15 % , b ) 20 % , c ) 10 % , d ) 8 % , e ) 22 %
[EX A]: d

[EX Q]: Problem: a car is purchased on hire - purchase . the cash price is $ 21 000 and the terms are a deposit of 10 % of the price , then the balance to be paid off over 60 equal monthly instalments . interest is charged at 12 % p . a . what is the monthly instalment ? 
Options: a ) $ 503 , b ) $ 504 , c ) $ 505 , d ) $ 506 , e ) $ 507
[EX A]:
b