The formula used for the "what-I-need-to-get" calculator: 

(a - (b * c))/(1 - b) = d  

where a is the end-of-term percentage you want, b is the portion of the course that has been completed, {expressed as a decimal, e.g., 22% would be "0.22"}, c is your current overall grade, and d is the percentage score you need to get on the remaining material to achieve want you want.

For example, if you desire a 90% (a) at the end of the term and your current overall grade is 80% (c) with 38% of the course completed (b), then: 

(90-(.38 x 80))/(1-.38) = 96.1  (i.e., you need a 96.1% on the remaining material)

Note: for ZOO 200, the portion of the course that has been completed is equal to the sum total of the relative values of the completed tests. For example, since the midterms are worth 14% and lab practicals 8%, then, after taking the first exam and lab practical, 22% (14% + 8%) of the course would be completed. This calculation may be the same for other courses, or this value may instead be a percentage which is equal to points completed divided by total points possible.