This is normal and it is to be expected. Problems which cannot be readily completed should be flagged, and the student should redo those problems at a later time. This process should be repeated until the problem is mastered. Although not collected nor graded, material from any assigned homework can be included on exams and in recitation activities. Bring a calculator to every exam and to every recitation meeting, and be certain it has a charge on it.
Dead batteries can be fatal.
Be certain you know how to use your calculator. A calculator capable of standard math functions and scientific notation is required for this course. Note that the ban is on calculators capable of this feature. Therefore, NO such calculator may be used, even though the memories have been erased. If a student is believed to be using a banned calculator, points can be deducted from their exam afterwards.