See if you can solve this simple problem:
A bat and ball cost $1.10.
The bat costs one dollar more than the ball.
How much does the ball cost?
Most people choose 10 cents. More than 50 percent of students at MIT, Harvard, and Princeton gave this intuitive answer. At less selective universities, more than 80 percent get it wrong. I sure did. Even after I knew the solution, the reasoning kept slipping away from me.
The correct answer is 5 cents.
Think it through slowly now. If the ball cost 10 cents and the bat cost a dollar more than the ball, that would mean you'd have to have $1.20 (10 cents for the ball and $1.10 for the bat for the bat to cost a collar more than the ball.)
But if the ball costs 5 cents, then you have $1.05. The bat costs a dollar more than the ball. You can get both the bat and the ball for $1.10.
"Going with your gut" is often a bad idea, argues economist Daniel Kahneman, who won the Nobel prize in 2002.
In his new book, "Thinking Fast and Slow," he uses the ball-and-bat problem to illustrate the perils of intuition.
"The voice of reason may be much fainter than the loud and clear voice of erroneous intuition," writes Kahneman, "and questioning your intuition is unpleasant."
Kahneman divides our thinking into two systems. System 1 is intuitive, fast and emotional. System 2 is calculating, slower, and logical.
Another problem is stereotyping:
Linda is 31 years old, single, outspoken and very bright. As a student, she was deeply concerned with issues of discrimination and social justice and also participated in anti-nuclear demonstrations.
Which is more likely?
• Linda is a bank teller.
• Linda is an insurance salesperson.
• Linda is a bank teller and is active in the feminist movement.
We often choose the option that Linda is a bank teller and active in feminist movements -- it fits our stereotypes.
But it is more likely that Linda is more likely to be a bank teller (the larger group) than a bank teller who is also active in feminist movements (the smaller group).
We can also come up with the wrong answer because of the "availability" error. We overestimate the number of instances that occur simply because these instances come more easily to mind.
Most of us believe that terrorist attacks, for example, are far more common than they are. Even in Israel, where people have good reason to fear terrorism, traffic deaths are far more frequent than deaths from terrorism.
Gruesome images of death from terrorism, endlessly broadcast in television and discussed, cause these deaths to come more quickly to mind.
System 2, the logical part of the brain, can also lead us astray. Kahneman tells the story of how he, as a psychologist, was supposed to make judgments about which soldiers were better suited to officer training.
He watched the soldiers solving a logistical problem. Some men took charge, those who seemed to be natural leaders.
Kahneman thought it was easy to make logical decisions about who had leadership skills. Yet his forecasts were largely useless.
The moral of this research is that we should rely on both intuition and reason in making an important decision. My husband and I, for example, made what nowadays we would call a snap decision.
He took a day to decide that he should marry me and I took three weeks. We have been married for over 44 years.
But our decision to marry was not only a snap decision. We had lots of experience in dating other people and when we found the right person, we knew it.
The moral of Kahneman's research is that better decisions are made when both intuition and reason work together.
Judith Kleinfeld is professor emeritus of psychology at the University of Alaska Fairbanks.