The probability of drawing a red marble on the first draw is 6/20. Since the marble is replaced, the probability remains the same for the second draw. The probability of drawing a red marble twice in a row is (6/20) x (6/20) = 36/400 = 9/100.

There are 6 x 6 = 36 possible outcomes when rolling a die twice. There are 6 outcomes that result in a sum of 7: (1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1). So, the probability is 6/36 = 1/6.

The number of boys playing basketball is 0.6 * 100 = 60. The number of girls playing soccer is 0.5 * 100 = 50. Thus, the total number of students participating in sports is 60 + 50 = 110. Subtract this number from the total number of students to find how many students don't play either sport: 200 - 110 = 90.

To find the average of the other 11 students' test scores, we need to find the sum of the 11 students' test scores. The sum of all 12 students' test scores is (mean) x n = 75 x 12 = 900. The sum of the 11 students' test scores is 900 - 100 = 800. The average is 800 / 11, which is approximately 72.7.

To determine the number of students who have not read either book, we can use the formula A∪B = A + B - A∩B, where A is the number of students who have read the first book, B those who have read the second, and A∩B those who have read both books. Thus, there are a total of 10 + 6 - 3 = 13 students who have read at least one of the books. This means that 30 - 13 = 17 students have not read either book.