David Kestenbaum

Each summer, as college students prepare to leave campus, they get rid of their textbooks, selling them for cheap. And Bob Peterson and Kenny Jacobson are waiting to buy them, and resell them when school is back in session and demand is high. Their scheme sounds simple, and it is. They've noticed a difference in price, and they're turning it into a quick profit.

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DAVID GREENE, HOST:

Note: This episode originally ran in 2015.

Note: This episode originally ran in 2015.

Hernando de Soto's parents always talked about Peru as he was growing up. His family had moved to Switzerland after a coup. They were kicked out of the country, and for many years de Soto thought of Peru as this magical place.

When he was 38, de Soto moved back to Peru. He knew the country was poor, but he didn't really understand the extent of the poverty until he got there.

Note: This episode originally ran in 2015.

Spreadsheets used to be actual sheets of paper. Sometimes, a bunch of sheets of paper taped together.

Any calculation made on a spreadsheet was done by hand, and these could take days to complete for an accountant or bookkeeper. It was tedious. One little adjustment to these calculations meant a whole day of erasing and filling the same boxes out again.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.