Which of the following pairs of class limits would be appropriate for grouping the numbers 12, 15, 10, and 17 ?
a. 9-13 and 13-17
b. 10-12 and 15-17
c. 10-12 and 13-17
d. 10-13 and 14-17

d. 10 -13 and 14 -17

Because:

1) the range of the values is 10 to 17 (inlcude 8 numbers), which divided by 2 is 4, and the range of the selected classes is 4, so you can have two class interval of the same size, which is what the option d represents..

2) all the values are included (some pair of intervals excluded some numbers)

The answer is 8 apex