In the first 4 papers each of hundred marks Ravi got 90, 75, 73, 85 marks.

If he wants an average of greater than or equal to 75 marks and less than

80 marks, find the range of marks she should score in the fifth paper.

Average of ravi’s marks = [90+75+73+85+V^th]/5

For average marks more than or equal to 75:

[90+75+73+85+V^th]/5  ≥ 75

[90+75+73+85+V^th] ≥ 75*5

[90+75+73+85+V^th] ≥ 375

V^th ≥ 375-[90+75+73+85]

V^th ≥ 375-323

V^th ≥ 52

For average marks less than 80:

[90+75+73+85+V^th] ≤ 80*5

V^th ≤ 400-323

V^th ≤77

So in order to obtain average marks more or equal to 75 and less than 80, ravi, needs to score minimum 52 marks and maximum 77 marks in his last exam.