Tính M M= 100.100-99.999+98.98- 97.97+ …+2.2 – 1.1

M= 100.100-99.999+98.98- 97.97+ …+2.2 – 1.1

=(100-99)(100+99)+(98-97)(98+97)+…+(2-1)(2+1)

=100+99+98+97+…+2+1

=(1+100).100:2

=5050