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.

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 find the average age, add up the ages of the siblings and divide by the number of siblings: (5+7+9+12)/4 = 33/4 = 8.25.

The total number of chocolates is 3 + 5 + 2 = 10. There are 2 mint chocolates, so the probability of choosing a mint chocolate is the number of successful outcomes (choosing a mint chocolate) divided by the total number of possible outcomes (choosing any chocolate). So, the probability is 2/10, which can be simplified to 1/5.

To find the median, we first arrange the scores in ascending order: 75, 80, 84, 91, 92. The median is the middle value in the ordered list, which is 84 in this case.