It took Marie 10 minutes to saw a board into 2 pieces. If she works just as fast, how long will it take for her to saw another board into 3 pieces?

If Marie takes 10 minutes to saw a board into 2 pieces, it means it takes her 10/2 = <<10/2=5>>5 minutes to saw each piece.

Therefore, it will take her 5 x 3 = <<5*3=15>>15 minutes to saw another board into 3 pieces. Answer: \boxed{15}.