【正确答案】[证明]  因为X与Y独立同分布，故
   P{a＜min(X ,Y})≤b}=P{min(X,Y)≤b}-P{min(X,Y)≤a},=1-P{min(X,Y)＞b}-[1-P{min(X,Y)＞a}]=P{min(X,Y)＞a}-P{min(X,Y)＞b}=P{X＞a，Y＞a}-P{X＞b，Y＞b}=P{X＞a}P{Y＞a}-P{X＞b}P{Y＞b}=[P{X＞a}]²-[P{Y＞b}]².