81+75+77+x>or equal to 70*4

233+x >orequal to 280

x>or equal to 47.

Solving this using common sense and no algebra, start with the fact that the student would have to get four scores of at least 70 in order to get a 70 for her final grade, right? You know this because 70 x 4 = 280, and 280 is the lowest possible total score she can get because her total score has to be divided by 4 exams (280 divided by 4 = 70).

The student has done better than 70 on all three exams so far, so you already know she can get less than 70 on the fourth exam and still pass. Add up those three scores: 81 + 75 + 77 = 233 and you see she already has 233 of the needed 280, so subtract 233 from 280. You get 47, which is the score needed to get a 70 because 81 + 75 + 77 + 47 = 280 divided by 4 scores.

This doesn’t help you learn algebra, but the common-sense approach is a good check on answers to problems you’ve solved using your knowledge of algebra.

(81+75+77+x)/4 is greater than or equal to 70

solve that for x

233+x=280

x is greater than or equal to 47 would be the answer…

81 + 75 + 77 = 233.

she needs at least a 43.