Problem Solving

There are 28 students in a class. The first student draws a line of length 'a' units on the black board of the class. The second student draws a line of length 'b' units (a is not equal to b) on the black board of the class. The third student draws a line whose length is the average of the lengths of the two lines that are drawn by the first and second student on the black board. The fourth student draws a line whose length is the average of the lengths of the lines that are drawn by the first, second and third student. This process of drawing lines on the black board continues till the twenty-eighth student of the class. How many students drew the line having the same length?

A) 5/12(a + b)
B) 28(a + b)
C) 26
D) 14
E) None of these
CA ans would be posted after some discussion