Problem 10.1. In an International Peace Congress, presidents of 40 different countries are to meet. The newspaper called “World News” wants to publish, on its cover page, photos of every handshake that will take place between every two presidents at the congress.

10.1.1. How many photos should the newspaper expect to fit on the cover page?
(a) 40 (b) 760 (c) 780 (d) 800 (e) 820 (f) 840

my answer: 40 x 20= 800

done here

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