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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _add_observation_to_means(self, xj, yj):
 """Update the means without recalculating for the addition of one observation."""

        self._mean_x_in_window = ((self.window_size * self._mean_x_in_window + xj) /
                                  (self.window_size + 1.0))
        self._mean_y_in_window = ((self.window_size * self._mean_y_in_window + yj) /
                                  (self.window_size + 1.0))