A student obtain75 %,80% and 85% in three subjects. If the marks of another subject is added, then his average cannot be less than

Marks obtained from three subjects out of 300 is 75 + 80 + 85 = 240 If the marks of another subject is added, then the marks will be ≥ 240 out of 400. ∴ Minimum average marks =2404=60%[When marks in the fourth subject = 0]