`B=1/2! +2/3! +3/4! +...+ 99/100!`
`B=`$\dfrac{2-1}{2!}$`+`$\dfrac{3-1}{3!}$`+`$\dfrac{4-1}{4!}$`+.....+`$\dfrac{100-1}{100!}$
`B=(2/2!+3/3!+4/4!+....+99/100!)-(1/2!+1/3!+1/4!+...+1/100)!`
`B=(1+1/2!+1/3!+1/4!+1/99!)-(1/2!+1/3!+1/4!+...+1/100!)`
`B=1-1/100!`
`B=99/100!`
Mà `99/100<1`
`=>A<1`