Margaret Penrose was a house pseudonym used by the Stratemeyer Syndicate.
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The Stratemeyer Syndicate was a publishing company that produced a number of mystery book series for children, including Nancy Drew, the Hardy Boys, the various Tom Swift series, the Bobbsey Twins, the Rover Boys, and others.
The name Margaret Penrose was used for: The Dorothy Dale series, The Radio Girls series (Later reprinted as The Campfire Girls series) and The Motor Girls series.
Margaret Penrose was a house pseudonym used by the Stratemeyer Syndicate