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How many people attended President Trump’s inauguration? How many people went to the Women’s March in Washington DC the next day? A fierce debate has been raging since last weekend about the numbers of people at each event. We explore the difficulties of counting people in a crowd and take you through what experts have to contend with to come up with their best guess. (image: Attendees line the Mall at Trump's Inauguration Day in Washington DC. Photo: Lucas Jackson/Getty Images)