Many candidates were not able to get the second equation by equating the frequencies to 20 ie 1 + 3 + 1 + m + 4 + n + 2 + 1 = 20 to get m + n = 8, even when they were able to get the first equation  5m + 7n = 44. Hence, they were not able to find the values of m and n.  Others divided ∑fx by 8 instead of 20.