What must be true and what letter is the answer?

School has 204 sixth grade students. if the sixth grade is 30% of the total school, how many students are in the middle school?

The difference between two numbers is one. three times the larger number minus two times the smaller number is 9. what are the two numbers

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.