Answer:
73
Step-by-step explanation:
to find the mean you need to add up all grades and divide if by the number of terms you added
(82 + 88 + x) ÷ 3 = 69 (since we don't know the third grade let's call it x)
170 + x = 69 × 3
x = 37
if the digits transposed the the actual grade would be 73