Answer:
#9: 5
#10: -2
#11: -1.5
Step-by-step explanation:
#9: 3,8,13,18,23,(28),(33),(38),.. Go up by 5 each time, so the common difference is 5.
#10: 11,9,7,5,3,(1),(-1),(-3),... Go down (-) by 2 each time, so the common difference is -2.
#11: 3, 1.5, 0, -1.5, -3, (-4.5), (-6), (-7.5),... Go down (-) by 1.5 each time, so the common difference is -1.5.
