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.

[EX Q]: Question: How many odd 4-digit positive integers R that are multiples of 5 can be formed without using the digit 3?

 Option A: 648

 Option B: 729

 Option C: 900

 Option D: 1296

 Option E: 3240
[EX A]: Option A

[EX Q]: Question: A man ran 20 miles in 2 hours 2 minutes. What was the average speed of the man in miles per hour?

 Option A: 9.72 miles / hour

 Option B: 9.73 miles / hour

 Option C: 9.75 miles / hour

 Option D: 9.78 miles / hour

 Option E: 9.79 miles / hour
[EX A]: Option D

[EX Q]: Question: Pipes A and B can fill a tank in 6 and 4 hours. Pipe C can empty it in 12 hours. If all pipes are opened together, then the tank will be filled in?

 Option A: 3hr

 Option B: 2hr

 Option C: 1hr

 Option D: 9/7hr

 Option E: 5/3hr
[EX A]:
Option A