19 + 199 + 1999 + 19999 + 1991 + 2 + 3 + 4 + +97+98+99+100.

19 + 199 + 1999 + 19999 + 1991 + 2 + 3 + 4 + +97+98+99+100.

19+199+1999+19999+199,=19+1+199+1+1999+1+19999+1+199+1-5,=20+200+2000+20000+200-5,=22420-5,=22415;1+2+3+4+… +97+98+99+100,=(1+100)×100÷2,=101×100÷2,=5050.