The average of your first 6 tests is 82. if your test average after your seventh test is an 80.5, what did you score on the seventh test?

question 2 options:

So average is  of the first 6 tests is 82   well that means 

(test1 + test2+ test3+ test4 + test5+test6)/6 = 82

so now let do some cross multiplliying 

test1 + test2 + test3 + test 4 + test5 +test6 = 82*6

test1 + test2 + test3 + test 4 + test5 +test6  = 492

now lets see if we can find that 7th test score

(test1 + test2 + test3 + test4 + test5 +test6 + test7)/7 = 80.5

So look we found test1 + test2 + test3 + test4 + test5 +test6 to be 492 so lets substitute. 

(492 + test7 )/7 = 80.5

test7 = (80.5*7)-492 = 71.5