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.

Question: A reduction of 20% in the price of salt enables a lady to obtain 10kgs more for Rs.100, find the original price per kg?

 Option A: Rs.3.2

 Option B: Rs.2.9

 Option C: Rs.2.5

 Option D: Rs.5.2

 Option E: Rs.2.1
Option C

Question: How much time will it take for an amount of Rs. 900 to yield Rs. 81 as interest at 4.5% per annum of simple interest?

 Option A: 2 years

 Option B: 3 years

 Option C: 1 year

 Option D: 4 years

 Option E: 5 years
Option A

Question: If money is invested at r percent interest, compounded annually, the amount of investment will double in approximately 70/r years. If Pat's parents invested $ 8000 in a long term bond that pays 8 percent interest, compounded annually, what will be the approximate total amount of investment 18 years later, when Pat is ready for college?

 Option A: $20000

 Option B: $15000

 Option C: $32000

 Option D: $10000

 Option E: $9000

Option C