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 can complete the job in 4 hours and B can complete the same job in 3 hours. A works for 1 hour and then B joins and both complete the job. What fraction of the job did B complete

 Option A: 1/7

 Option B: 3/10

 Option C: 1/2

 Option D: 5/6

 Option E: 8/9
Option A

Question: A cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?

 Option A: 2.9 hrs

 Option B: 4.5 hrs

 Option C: 2.9 hrs

 Option D: 7.2 hrs

 Option E: 8.6 hrs
Option B

Question: The simple Interest on a certain sum of money at the rate of 4% p.a. for 5 years is Rs. 1680. At what rate of interest the same amount of interest can be received on the same sum after 4 years ?

 Option A: 5%

 Option B: 6%

 Option C: 8%

 Option D: 4%

 Option E: 7%

Option A