Answer:
86
Step-by-step explanation:
Firstly,
Average = Sum/Number of Numbers
Since 7 grades' average is 77, so we can say:
77 = Sum/7
Hence, Sum = 77 * 7 = 539
Now,
81 - 18 = 63 [63 marks were recorded incorrectly. actual sum would be 63 more]
So,
Actual Sum should be 539 + 63 = 602
Actual Average = 602 / 7 = 86
Hence, actual report card average would be 86