How about this for an equation to put a spring in a step of aspiring entrepreneurs everywhere? It couldn’t be simpler: three business-course students + one good idea = $1 billion.

That’s the estimated value of Sweetgreen, a chain of fast-food restaurants specialising in bowls of salad that was set up 13 years ago by Nathaniel Ru, Jonathan Neman (below right) and Nicolas Jammet (below left), three friends who met when they were studying business at Georgetown University in Washington DC.

They recently told the BBC’s news website the story of how, frustrated by their inability to find a local restaurant that served food that was both inexpensive and healthy, the then students drew up a preliminary business plan in their college dorm room. After inviting friends round for taste tests -“We even had this little anonymous surveys people could fill out,” Jammet recalls – a year later they opened their first branch of Sweetgreen in a disused pub near their Georgetown campus.

The idea took off almost immediately, and although the trio initially struggled to find the capital to allow them to expand, eventually some forward-thinking investors stepped forward and now 90 branches of Sweetgreen can be found right across the USA.

In retrospect, the trio understand why initially investment was so hard to come by. “We had no track record, no resume — we were just kids from college,” remembers Neman, now CEO. Nor did they originally envisage their idea becoming a nationwide phenomenon. “We didn’t think it would turn into a career,” he says. “We just saw it as a way to solve a problem, because there was such a need for healthy food. We thought we would open one restaurant and then do something else.”

A foodie story to nourish the dreams of business students around the globe.