### Possible Answer

excellent answer above me, but i dont get how he got percentages? i cant work it out on my own. - read more

Based on normal model of a distribution: Mean = 20 45% is above 30 Find standard deviation of model. - read more

Please vote if the answer you were given helped you or not, thats the best way to improve our algorithm. You can also submit an answer or search documents about how to find percentage when given standard deviation and mean.