果园里有桃树850棵，比杏树棵树的3倍多28棵．杏树有多少棵？
（850-28）÷3
=822÷3
=274（棵），
答：杏树有274棵．
长于治疗寒痰咳喘，胸满胁痛的药物是（）
A.白芥子
B.紫苏子
C.杏仁
D.葶苈子
E.桔梗
Dispersion is defined as the variability around the central tendency and can be divided into absolute dispersion and relative dispersion. Which of the following is NOT described as a measure of relative dispersion（）
A. Range.
B. Sharlle ratio.
C. Coefficient of variation.
