There is a company X that does not elect employees who are under 20 ye

Yes it is. In fact if you look at the statement "There is a company X that does not elect employees who are under 20 years old". that means 100% of the employee are of age 20 years or older, not just 10%. I have solved the question based on certain assumptions

OFFICIAL EXPLANATION

If you modify the original condition and the question, and assume that the total number of employees is 100, the question becomes “is the average age of the employees older than 30 years old?” This becomes the sum of the 100 employees’ ages > (30 years old)(100 employees) = 3,000 years old? And if you assume the minimum 10% as 20 years old, you get 10 employees * 20 years old = 200, which becomes the sum of the rest 90 employees’ ages > 3,000 years old – 2,00 years old = 2,800 years old? Then, 

for con 1), if it is 70% of the employees, it is 70, and (70)(40 years old) = 2,800 years old, so it is greater than 40 years old, hence yes, it is sufficient. 

For con 2), you should apply CMT 4 (B: if you get A or B too easily, consider D). If you assume that 75% of the total employees are all 20 years old and the rest 25% are 60 years old, the sum of total 100 employees’ ages = (75 employees)(20 years old) + (25 employees)(60 years old) = 3,000 years old, and since 75% is older than 60 years old, it is always yes and sufficient. Therefore, the answer is D.

Hi, I'm relatively new to GMAT, and everybody seems to be using this "CMT" strategy, could you please send me a link where I can read more about this.

MathRevolution, Could you help to explain?

avinsethi, only mathrevolution official explanation using that strategy. I am not familiar with that as well.

This question needs rewriting!!
The logic of the question doesn't even stand!