Question 692911: If my average for a class is 79%. What would I need to get on my 30% final in order to have at least a grade of 60% overall?
Answer by RedemptiveMath(80)   (Show Source):
You can put this solution on YOUR website! These problems may be tricky if you are not used to solving them. Let's use variables to set up an equation that determines what your final grade will be based on what you get on the final. Before we determine that equation, let us try to formulate what we are dealing with into words:
Current grade percentage * weight of all other assignments + grade desired on final exam x weight of final exam = final grade desired.
Plugging in the numbers that we already have and using a variable for the one we don't:
79%(.7) + 30%(x) = 60%
0.79(.7) + 0.3x = .6.
Now we can just solve for x to find what the percentage must be in order for the final grade to be 60%.
0.79(.7) + 0.3x = .6
0.553 + 0.3x = .6
0.3x = 0.047
x = 0.156667 (approx.) or about 15.67%.
The reasoning for how we arrive at this equation is simple. We first have our current grade of 79%. Next we have to deal with the weight of the grade we have now. Since the weight of the final exam is 30% (assuming that is the only one this grading period), that means all of the other assignments must combine to have a weight of 70%. We can operate on our current grade and the weight of the assignments of that current grade because they both consist of the same parts (all of the assignments you have done before the final). Then we have multiply the weight of the final with the grade of the final, or 0.3x. After that we add the current grade's parts and the final exam's parts together. Finally, we set them equal to the grade we desire. This grade we desire limits what the grade of the final must be.
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