You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[Q]: Question: Three persons invested Rs.9000 in a joint business. The second person invested Rs.1000 more than the first and the third Rs.1000 more than second. After two years, they gained Rs.5400. How much third person will get?

 Option A: Rs.2400

 Option B: Rs.3600

 Option C: Rs.2850

 Option D: Rs.2000

 Option E: Rs.3000
[A]: Option A


[Q]: Question: The number of diagonals of a polygon of n sides is given by the formula z=n(n-3)/2. If a polygon has twice as many diagonals as sides, how many sides does it have?

 Option A:  3

 Option B:  5

 Option C:  6

 Option D:  7

 Option E:  8
[A]: Option B


[Q]: Question: here are 6 periods in each working day of a school. In how many ways can one organize 5 subjects such that each subject is allowed at least one period?

 Option A: 1235

 Option B: 4510

 Option C: 1203

 Option D: 1800

 Option E: 4512
[A]:
Option D