Picture a quiz. A bat and a ball cost one pound ten together. The bat costs one pound more than the ball. How much is the ball? A number has already arrived in your head, and for most people it is ten pence. Hold it there for a moment.
A question→The fast guess: free, instant→The slow check: costs effort
A mind answers in two speeds. The fast guess arrives on its own, in under a second, and it feels like knowing. The slow check has to be started on purpose. It costs effort, and it is the only one of the two that can find a mistake.
The ball? pence
++
The bat100 pence more
Check the guess. If the ball is ten pence, the bat is one pound ten, and together they are one pound twenty. Too much. What does the ball really cost, in pence?
pence
Together they are 110 pence. Take off the 100 pence the bat has extra, and split what is left between the two.
Right. Five pence. The bat is then one pound five, and together they make one pound ten. The fast guess took the one pound as the bat's whole price, which is the easy question it thought it had been asked.
Students at top universities
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All three rightunder half
A 2005 study put three questions of this kind to more than 3,000 people. Nearly everyone who did not say ten pence said five, so the fast answer and the right answer were the only two. At one of the world's top engineering universities, under half the students got all three right.
Slide the marker to the share of students at MIT, a top US engineering university, who got all three questions right in the 2005 study.
Slide the marker to where you think the answer is, then press Lock. Nothing is scored.
12
your guess · 0%
the answer · 48%
0%50%100%
1A quarter25%
2Three quarters75%
Your guess: —
Under half, 48 in 100, at a university whose students are picked for their exam marks. At a less selective university, 64 in 100 got none of the three. Guesses often land high, because the questions look too easy to catch anybody. The easy-looking question is the one the slow check never gets started on.
Looks easy, is easythe guess is fine
vsvs
Looks easy, is notthe guess answers the wrong question
The fast guess is not stupid. It is right nearly all the time; it is how a person walks, talks and catches a ball. It goes wrong in one kind of case: a question that looks easy and is not. The fast guess answers the easy question it thinks it saw.
What is 2 plus 2?
++
If 5 machines make 5 toys in 5 minutes, how long do 100 machines take for 100 toys?
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What colour is the sky?
Which of these questions is the fast guess most likely to get wrong?
Two plus two. Sums are where guesses go wrong.
Not yet. Two plus two is a sum the fast guess has done ten thousand times, and it gets it right every time. The trap is not sums; it is a question wearing the wrong shape.
The sky. Colours are a matter of opinion.
Not yet. The sky question has an obvious answer and no hidden shape, so the fast guess is fine. Opinion is not what makes the fast guess fail; a disguise is.
The machines. It looks like a times-table and is not.
Right. The fast answer is a hundred minutes, because the numbers line up. Each machine takes five minutes for one toy, so a hundred machines take five minutes. The shape of the question hid the easy sum.
Each is a job for the mind. Is it one the fast guess does well, or one that needs the slow check?
One card at a time. Tap the pile it belongs to.
Card 1 of 6
Catching a ball somebody throws to you.
Working out whether a headline is true.
Reading whether a friend is upset from their face.
Deciding if a deal that saves you money really does.
Noticing a car coming before you cross.
Checking a sum on a bill you think is too high.
Catching a ball somebody throws to you. → Fast guess
Not yet. Fast guess. The hand is in place before any thought could be, and it is nearly always in the right place.
Working out whether a headline is true. → Slow check
Not yet. Slow check. The fast guess has already said whether the headline feels true, and feels true is what lesson 1 was about.
Reading whether a friend is upset from their face. → Fast guess
Not yet. Fast guess. A face is read in a fraction of a second, and the reading is usually right.
Deciding if a deal that saves you money really does. → Slow check
Not yet. Slow check. A deal is built to look easy, which is the exact shape the fast guess gets wrong.
Noticing a car coming before you cross. → Fast guess
Not yet. Fast guess. The alarm fires before the thought, and here that is what keeps a person alive.
Checking a sum on a bill you think is too high. → Slow check
Not yet. Slow check. The feeling that it is too high is the fast guess; the sum is the check that can find out.
3Fast guess
vsvs
3Slow check
Right. Three are jobs the fast guess was built for, and it does them well. Three are questions that only look like those jobs, and they need the check started on purpose.
The guess arrivesin a second
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Feels sureat the same moment
The feeling of being sure comes with the fast guess. It arrives at the same moment, before any check has run. So the feeling says that the guess came easily. It does not say that the guess is right. Ten pence came very easily.
Half the lakeday ?
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The whole lakeday 48
A quiz: a patch of lily pads doubles every day and covers a lake in 48 days. When did it cover half the lake? The number 24 arrived at once. What is 24?
A fast guess. If it doubles daily, half the lake was the day before it was full: day 47.
Right. Half of 48 is 24, which is the easy question the guess answered. The real question is about doubling, and doubling means the last day did half the work.
The answer. Half the lake takes half the time.
Not yet. That is the fast guess talking, and it answered a question about halves. The patch doubles, so on day 47 it was half the size it was on day 48.
A rough answer. The real one is near 24 but needs a calculator.
Not yet. No calculator is needed; the slow check is one sentence. The day before full was half full. The guess was not rough; it answered the wrong question.
Lesson complete
A fast guess arrives on its own and feels like knowing. A slow check has to be started on purpose.