Question

There are 17 students in a class. on the day the test was given, john was absent. the other 16 students took the test, and their average score was 77. the next day, john took the test, and with his grade included, the new average is 78. what is john's grade on the test

Answer 1

Let x be the John's grade. 
The new average is 78 then we get the equation:
$\frac{16\times77+x}{17}=78\text{ We will solve like this:}\\ 16\times77+x=17\times78=1326\\x=1326-1232=94$

John graded 94.