=3x0.25+0.25x24.5+25.5x0.25=（3+24.5+25.5）x0.25=53÷4=13.25
(一3)x(一1/4)十0.25x24.5十(一51/2)x(一25%)=（-3-24.5-51/2）x(一1/4)=-63x(一1/4)=63/4
