4/5*4+2/5*4+1/5*16 =(4/5+2/5+1/5*4)*4 =(4/5+2/5+4/5)*4 =2*4 =8
原题=4/5×4+2/5×4+1/5×16=16/5+8/5+16/5=40/5=8
五分之四十