John  averaged  82  out  of  100  on  his  first  three  tests.    what  was  john’s  score  on  the  fourth  test  if  his  average  after  the  fourth  test  dropped  to  79  out  of  100?     a)  cannot  be  found    b)  80      c)  75        d)  70  can somebody me with this question, i know the right answer is 70 but what i don't know is how to do it. asap.

So on his first 3 test his total was 82/100
After his fourth test his total dropped to 79/100

So when you add the fourth test and the first 3 together they should average out to 79/100

We can solve this with trial and error
Because they are both out of 100 we just have to add them and find the average (which should be 79)

82+80= 162/2 = 81 so B is not the correct answer

82+75=157/2= 78.5 which would round up to 79
Therefore C, 75 is the correct answer.