What invention led to more women working in offices in the early 1900s?

The invention of the typewriter led to more women who became employed in offices. They were found to be better typists than men. A few women had been going into medicine since Elizabeth Blackwell became the first woman to graduate from a US medical school in 1849 these numbers increased after 1849.

Women had been working in factories since the Industrial Revolution started due to having small hands that made it easy to do smaller tasks, and had been going into teaching in large numbers since the 1840s. Many women worked as sales clerks, and nursing had been an increasingly popular occupation over time.