[tex]27\cdot12 =27\cdot(10+2)= 27\cdot10 + 27\cdot2 = 270 + 54 = 324\\\\31\cdot22 =31\cdot(20+2) = 31\cdot20 + 31\cdot2 = 620 + 62 = 682\\\\62\cdot14 = 62\cdot(10+4) =62\cdot10 + 62\cdot4 = 620 + 248 = 868\\\\25\cdot24 = 25\cdot(20+4) = 25\cdot20 + 25\cdot4 = 500 + 100 = 600\\\\35\cdot15 = 35\cdot(10+5) = 35\cdot10 + 35\cdot5 = 350 + 175 = 525\\\\13\cdot31 = 13\cdot(30+1)=13\cdot30 + 13\cdot1 = 390 + 13 = 403[/tex]
