Let A = {x1, x2, . . . , x12} be a set of 12 positive integers, not necessarily distinct, such that xi ≤ 150, 1 ≤ i ≤ 12. Prove that there are at least two different 6-element subsets S1 and S2 of A such that the sum of the elements in S1 is equal to the sum of the elements in S2. Use Pigeonhole principal.

The accompanying normal probability plot was constructed from a sample of 30 readings on tension for mesh screens behind the surface of video display tubes used in computer monitors. does it appear plausible that the tension distribution is normal? the given probability is has a significant downward curve, so it is plausible that the tension distribution is normal. the given probability is has a significant downward curve, so it is not plausible that the tension distribution is normal. the given probability is quite linear, so it is plausible that the tension distribution is normal. the given probability is has a significant upward curve, so it is not plausible that the tension distribution is normal. the given probability is quite linear, so it is not plausible that the tension distribution is normal.