kill two birds with one stone
kill two birds with one stone {v. phr.}
To succeed in doing two things by only one action; get two results from one effort.
Mother stopped at the supermarket to buy bread and then went to get Jane at dancing class; she killed two birds with one stone.
The history teacher told us that making an outline kills two birds with one stone; it makes us study the lesson till we understand it, and it gives us notes to review before the test.
Categories:
Source: A Dictionary of American Idioms