SOLUTION: If Joe gets 97 on his next math test, his average will be 90. If he gets 73, his average will be 87. How many tests has Joe already taken? Formula: T+97 = 90, T+73 = 87

Algebra ->  Average -> SOLUTION: If Joe gets 97 on his next math test, his average will be 90. If he gets 73, his average will be 87. How many tests has Joe already taken? Formula: T+97 = 90, T+73 = 87       Log On


   

Question 546758: If Joe gets 97 on his next math test, his average will be 90. If he gets 73, his average will be 87. How many tests has Joe already taken?
Formula: T+97 = 90, T+73 = 87
n+1 n+1
Answer by JBarnum(2146) About Me  (Show Source):
You can put this solution on YOUR website!
%28%28T%2B97%29%2F%28n%2B1%29%29=90
solve above for T
%28T%2B97%29=90%28n%2B1%29
T=90n%2B90-97
T=90n-7
use substitution below
%28%28T%2B73%29%2F%28n%2B1%29%29=87
%28%28%2890n-7%29%2B73%29%2F%28n%2B1%29%29=87
%2890n-7%2B73%29=87n%2B87
90n%2B66=87n%2B87
3n%2B66=87
3n=21
n=7
use substitution below
T=90n-7
T=90%287%29-7
T=623
check
%28623%2B97%29%2F%288%29=90
90=90
correct
check
%28623%2B73%29%2F%288%29=87
87=87
correct
he has already taken 7 tests