Question

the average marks of 18 students was calculated to be 65 however it was later found out that the marks of one student has been wrongly entered as 24 instead of 34 end of another 88 instead of 78 find the correct average

Answer 1

Find the sum of the marks of 18 students :

Average = 65

Sum = 18 x 65 = 1170

Take away the wrong marks:

1170 - 24 - 88 = 1056

Add back the correct marks:

1056 + 34 + 78 = 1170

Find the correct average:

Sum = 1170

Average = 1170 ÷ 18 = 65

Answer: The average is still 65.

Answer 2

18 students = 65, Sum = 18 x 65= 1170,

Mis entered wrongly = 24 instead of 34 and 88 instead of 78,

Take away the wrong marks = 1170 - 24-88= 1056,

Add the correct marks = 1056+ 34+78= 1170, Average = 18