tính hợp lý
c1, -56+8(11+7)
c2, 47(23+50)-23(47+50)
c3, 85(47-29)+29(85-47)
c4, (-16)(-25)(-12)
c5, -19(16-25)+19(25-4)
c6, 11(16+24)+24(11-16)
c7, 29(85-47)-23(15-29)
c8, 15(23-29)+23(15-29)
c9, 13(55-29)-55(13-29)
c10, 37(27+25)+72(-25)
c11, (-216).68+32(-312)
c12, 44(-50)-50.56
c13, -69(-4).2-3(-7)(-2)
c14, 25.11.(-15)-50.15(-5)
c15, 47.69+31.(-47)