instruction:
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:
Question: Which of the following CANNOT be weighed using a balance scale and these unit weights: 1, 4, 7, and 10

Option A: 13

Option B: 15

Option C: 17

Option D: 19

Option E: 21
answer:
Option A

question:
Question: In how many ways, a committee of 5 members can be selected from
6 men and 5 ladies, consisting of 3 men and 2 ladies?

Option A: 100

Option B: 200

Option C: 300

Option D: 400

Option E: 500
answer:
Option B

question:
Question: The average of 9 observations was 4, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?

Option A: 54

Option B: 12

Option C: 15

Option D: 17

Option E: 18
answer:
Option A