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: The probability that a visitor at the mall buys a pack of candy is 30%. If three visitors come to the mall today, what is the probability that exactly two will buy a pack of candy?

 Option A: 343

 Option B: 147

 Option C: 189

 Option D: 063

 Option E: 027
[EX A]: Option C

[EX Q]: Question: Which of the following is NOT a factor of 10! ?

 Option A: 1440

 Option B: 625

 Option C: 160

 Option D: 80

 Option E: 50
[EX A]: Option B

[EX Q]: Question: 2 persons allotted to one work. John can do piece of work in 30 days while Bruce alone can do it in 40 days. In how many days can John and Bruce working together to do it?

 Option A: 17 2/7days

 Option B: 17 1/7days

 Option C: 17 3/5days

 Option D: 18 1/7days

 Option E: 17 1/4days
[EX A]:
Option B