The mark obtained by 30 students in Mathematics in the annual examination are given below: 42, 31, 27, 60, 61, 42, 35, 58, 29, 48, 39, 52, 40, 47, 28, 78, 90, 52, 48, 36, 52, 39, 71, 32, 48, 56, 29, 33, 25, 48. Find the mode of the marks -