Final answer:
Each option provided (50, 60, 70, 80) is a number between 31 and 100; however, the exact middle is 65.5, which is not listed among the options.
Step-by-step explanation:
The student is asking for the number that is between 31 and 100. All the options given (50, 60, 70, and 80) fall within this range, so technically any of them could be a correct answer.
To provide the exact middle point, we can calculate the average of 31 and 100, which is (31+100)/2 = 65.5.
Therefore, the number that is exactly in the middle between 31 and 100 is 65.5.
However, since this number is not one of the options and the closest provided options are either 60 or 70, we may guess the question asks for a more general ‘middle’ number. In such a case, any of the numbers provided could be considered to be between 31 and 100.