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: If a man crosses a 600 m long street in 5 minutes. What is his speed?

Option A: 7 km/hr

Option B: 7.1 km/hr

Option C: 7.2 km/hr

Option D: 8 km/hr

Option E: 8.5 km/hr
Option C

Question: Two pipes A and B can fill a cistern in 20 and 30 minutes respectively, and a third pipe C can empty it in 40 minutes. How long will it take to fill the cistern if all the three are opened at the same time?

Option A: 17 1/5

Option B: 17 1/8

Option C: 17 1/7

Option D: 17 1/1

Option E: 17 1/2
Option C

Question: There are two inlets and one outlet to a cistern. One of the inlets takes 4 hours to fill up the cistern and the other inlet takes twice as much time to fill up the same cistern. Both of the inlets are turned on at 8:30 AM with the cistern completely empty, and at 10:30AM, the outlet is turned on and it takes 1 more hour to fill the cistern completely. How much time does the outlet working alone takes to empty the cistern when the cistern is full?

Option A: 2 hours

Option B: 2.5 hours

Option C: 3 hours

Option D: 3.5 hours

Option E: 8 hours
Option E