Вычислите с объяснением и проверкой 60-29, 27+54, 45+34, 76-18, 31-15, 23+49, 90-12, 56+32

60-29=(50-20)+(10-9)=30+1=31, пр.: 31+29=30+20+1+9=60;27+54=20+50+7+4=81, пр.: 81-27=(70-20)+(11-7)=50+4=54;45+34=40+30+5+4=79, пр.: 79-34=(70-30)+(9-4)=40+5=45;76-18=(60-10)+(16-8)=50+8=58, пр.: 58+18=50+10+8+8=76;31-15=(20-10)+(11-5)=10+6=16, пр.: 16+15=10+10+6+5=31;23+49=20+40+3+9=72, пр.: 72-23=(60-20)+(12-3)=40+9=49;90-12=(80-10)+(10-2)=70+8=78, пр.: 78+12=70+10+8+2=90;56+32=50+30+6+2=88, пр.: 88-32=(80-30)+(8-2)=50+6=56.