Leonard Mlodinow split the Newman Auditorium, which was packed and had more than 15 people turned away at the door, into two groups at 7 p.m. on Feb. 8. One group guessed there were between 20 and 30 countries in Africa, while the other guessed 60 to 70 countries. Why the huge difference?

Mlodinow, author of “The Drunkard’s Walk: How Randomness Rules Our Lives,” used an idea called anchoring. He asked one group to turn away while the other wrote down answers to the following questions: are there less than 180 countries in Africa? How many countries are there in Africa? This group answered there are between 60 and 70 countries in Africa.

Mlodinow, who has a doctorate in theoretical physics from UC Berkeley, asked the next group if there were more than 20 countries in Africa and how many countries there are. This group answered there are 20-30 countries in Africa.

There are 54 countries in Africa. The experiment demonstrated how numbers influence a person. Those who were asked if Africa had 20 or more countries guessed lower than those who were asked if Africa had less than 180.

Mlodinow first talked about his book “The Drunkard’s Walk,” then about his new book called “Subliminal,” which deals with ideas like influencing people’s ability to judge by introducing phony data. “The Drunkard’s Walk” is concerned primarily with randomness and how much it runs our lives.