I am deeply confused by the Triangle Inequality Theorem, how come it doesn't work for 3-1-2? I mean when you add 3 and 1 you get 4 and 4 is greater than 2... so why doesn't it work? Am I missing something?

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.