The marks obtained by six students in a test are 12, 25, 18, 18, 20, The number of students whose marks are more than the average marks is

The correct answer is (b).

To find the average marks, we add up all the marks and divide by the number of marks. In this case, the average marks are $\frac{12+25+18+18+20}{6}=\frac{93}{6}=15.5$.

There are 2 students whose marks are more than the average marks: 25 and 20.

(a) is incorrect because only 1 student has a mark more than the average mark.
(c) is incorrect because 3 students have marks less than the average mark.
(d) is incorrect because there are only 6 students, so there cannot be 4 students whose marks are more than the average marks.