98-154+269+787
=100-2-150-4+250+19+800-13
=(100+800)+(250-150)+(19-13)-(2+4)
=900+100+6-6
=1000
98➖154➕269➕787
=100-2-154+300-31+800-13
=100+300+800-(154+2+31+13)
=1200-200
=1000
98-154+269+787
=100-2-160+6+270-1+800-13
=(100-160+270+800)+(-2+6-1-13)
=1010-10
=1000
原式=1154-154
=1000.