Question 749364
Hi John
If the first 5 tests gave an average of 8
then the totals for the 5 tests were 40 (5 x 8)
If his next two tests scored 7 and 5 then his 
total now becomes 52 (40 + 7 + 5).
His eighth test brought his average to 7.5
so his total of marks was 60 (8 x 7.5)
Taking 52 away from 60 = 8 his score for the eighth test.
Hope this helps mate.
:-)