再请教几道化学真题，谢谢

远地点UID: 2651690

analysis of a bottle of 100 mg vitamin C tablets yields an average vitamin C content og 99.8 mg, with a standard deviation of +- 0.3 mg. Assuming Gaussian statistics, which of the following is true?

答案是 68% of the tablets contain between 99.5 and 100.1 mg of of vitamine C

不明白，68%是怎么算出来的。请高手解释解答方法。谢谢

SakurawindUID: 2378663

you don't need to do calculations, just remember the rule...
99.5 and 100.1 lie in (+-) 0.3 between the average value 99.8 (so 100 is of no use in cracking this question)
About 68% of the values lie within 1 standard deviation of the mean.

this is called the three-sigma rule.(相信很多人都听过的"3σ"法则!!)
by the way, about 95% of the values lie within 2 standard deviations of the mean.
Nearly all (99.7%) of the values lie within 3 standard deviations of the mean.

so猫UID: 148633

it's the famous 68-95-99.7 rule in statistics
http://en.wikipedia.org/wiki/Sta ... ly_distributed_data

juggernautsUID: 2897057

正态分布手册有。0.6827这个值要记得~

erinceUID: 2813370

:L
0.6826
0.9544
0.9974