265十199=265十20O一1=465一1=464876一298=876一300十2=576十2=578
265 +199=265+(200-1)=265+200-1=465-1=464
265+200-1＝464876-300+2＝578
628-199 =628-200+1 =428+1 =429 298+376 =300+376-2 =676-2 =674
