TASK DEFINITION: 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.
PROBLEM: Question: The number of diagonals of a polygon of n sides is given by the formula z=n(n-3)/2. If a polygon has twice as many diagonals as sides, how many sides does it have?

 Option A:  3

 Option B:  5

 Option C:  6

 Option D:  7

 Option E:  8

SOLUTION: Option B

PROBLEM: Question: What is the units digit of 18! + 5 ?

 Option A: 2

 Option B: 3

 Option C: 4

 Option D: 5

 Option E: 6

SOLUTION: Option D

PROBLEM: Question: On a windy day, out of every 3 sand dunes formed, only 1 remains. Out of 5 blown-out
sand-dunes, 1 has treasure and only 2 out of 3 sand dunes formed have lucky coupons. Find
the probability that the blown-out sand dune will contain both the things.

 Option A: 2/25

 Option B: 4/75

 Option C: 7/75

 Option D: 3/5

 Option E: 4/45

SOLUTION:
Option E