1)9/20÷0,09+3,61÷1/5-18,63=0,45÷0,09+3,61÷0,2-18,63=5+18,05-18,63=23,05-18,63=4,42
2)(2 1/2-1,805)÷1,39+4÷2,5=(2,5-1,805÷1,39+1,6=0,695÷1,39+1,6=0,5+1,6=2,1
3)19,5÷(3,5-1,55)-0,555÷0,15=19,5÷1,95-3,7=10-3,7=6,3
4)91×0,4÷5,6+3,48÷0,24×1,8=36,4÷5,6+14,5×1,8=6,5+26,1=32,6