The average salary of a person for the months of January, February, March and April is Rs.8000 and that for the months February, March, April and May is Rs.8700. If his salary for the month of May is Rs.6500, find his salary for the month of January?
Choose the correct choice from the following options:  A) s . 3700  B) s . 4570  C) s . 4500  D) s . 4550  E) s . 2500

Rationale: "sum of the salaries of the person for the months of january , february , march and april = 4 * 8000 = 32000 - - - - ( 1 ) sum of the salaries of the person for the months of february , march , april and may = 4 * 8700 = 34800 - - - - ( 2 ) ( 2 ) - ( 1 ) i . e . may - jan = 2800 salary of may is rs . 6500 salary of january = rs . 3700 answer : a"
Answer: A