1. S101=101*a1+101*100*(-1)/2=10100-10100=0 2. an=a1+(n-1)d 100=20+n-1 n=79 S=(a1+an)*n/2 =60*79=4740
840÷40=÷008600÷20=8÷08107×100=-880×30=÷0S101×101=÷0S840÷14=÷0S163×67=8×0S190×30=÷080250÷50=×0814500÷900=0540÷27-÷005600÷700=001246÷41=÷00S480÷40=÷82400÷20=÷0S13200÷40=0S360÷12=÷008420÷21=÷000450÷90=×0S560÷28=÷048540÷30=÷000480÷24=...