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'.

Q: Problem: what will be the difference between simple and compound interest @ 20 % per annum on a sum of $ 500 after 2 years ? 
Options: a ) $ 10 , b ) $ 20 , c ) $ 25 , d ) $ 30 , e ) $ 40

A: b
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Q: Problem: find the c . i . on a sum of rs . 10000 for 6 months at 20 % per annum , interest being compounded halfyearly ? 
Options: a ) 3010 , b ) 2010 , c ) 1000 , d ) 3100 , e ) 2100

A: c
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Q: Problem: a pair of articles was bought for $ 1000 at a discount of 10 % . what must be the marked price of each of the article ? 
Options: a ) $ 555.55 , b ) $ 500 , c ) $ 350 , d ) $ 400 , e ) $ 600

A:
a
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