Weight(gm) frequency
125-180 1
180-235 8
235-290 11
290-345 43
345-400 20
400-455 15
455-510 2

Using this frequency distribution when I calculate the moment based measures of skewness gamma1; it comes that the distribution is left skewed.but when use Kelly's measures of skewness(parcentile based);it comes the distribution is negatively skewed