import math


def find_t(X1, X2, S1, S2, N1, N2):
  """X1 and X2 are means, S1 and S2 std devs, N1 and N2 are
     population sizes (and not degrees of freedom)
  """
  #with this, the result between scipy and manual is the same
  N1 = N1 - 1
  N2 = N2 - 1
  above = (X1 - X2)
  below = math.sqrt(  ((S1**2)/N1)  +  ((S2**2)/N2)  )
  return above/below