Problem 1
  2*100*10+0=
  2*100*10-0=
  2100-100=
Problem 2
  IMPOSSIBLE
Problem 3
  4+1*1996=
  4*1+1996=
Problem 4
  2*1000+0+0=
  2*1000+0-0=
  2*1000+0*0=
  2*1000-0+0=
  2*1000-0-0=
  2*1000-0*0=