Considering U1 and U2 which both follow Uniform (0 , A), then after
the transformation of variable, i can find x=(U1+U2)/2 has f(x)=2/A(both
my classmates and me get this result). However i am confused that when i
integrate x by it range from 0 to A (because U1 and U2 both ranged from
0 to...