Find the exam score needed to reach a target grade.
The work already graded has banked a fixed number of percentage points towards the final grade — your current grade times the share of the course it covers. Everything else has to come from the exam, so the score required is the shortfall divided by the exam's weight. Dividing by a small weight is what produces the impossible numbers students sometimes see: with the exam worth 20 percent, every point of shortfall needs five points on the exam. The best and worst still-possible grades bound the outcome regardless of how the exam goes.
Banked points
Banked = current grade x share of course already graded
Required score
Required exam score = (target grade - banked points) / exam weight
Because the target is arithmetically out of reach with the weight remaining. The honest response is to reset the target to the best-possible figure shown rather than to hope for the impossible.
Not necessarily — there may be other ungraded work. Enter them accurately: if graded work covers 70 percent and the exam is 30, they sum to 100 and nothing else is outstanding.