Write and solve an equation to find the value of the variable. 5.2, 8.3, 8.5, 7.7, 7.8, y; mean = 7.1

Mean of a set of numbers is the quotient when their sum is divided by the number of items in the set. For the given above, their sum (S) is, 
                        S = 5.2 + 8.3 + 8.5  + 7.7 + 7.8 + y = 37.5 + y

The mean (m) is calculated through the formula, 
                                  m = S / n 
where n is the number of items. In this given there are 6 items including y. 
                                7.1 = (37.5 + y) / 6   ; y = 5.1

Therefore, y is equal to 5.1.