Spencer Tirey/Getty Images
Gary Stevenson, the author of "The Trading Game," spent his early 20s trading trillions of dollars for Citibank in London and Tokyo.
SAUL LOEB/Getty Images
Momo Takahashi
Citigroup; Getty Images; Alyssa Powell/BI
Michael M. Santiago/Getty Images; Getty Images; BI
Andrew Harnik/Getty Images

The banking industry took its time to transition from paper bills to plastic cards. Now it’s in the midst of a more rapid transformation: going digital.