Can you solve this logic quiz?

Harvard cognitive psychologist Steven Pinker has a new book, Rationality, in which he makes the case that our gut instincts are often, if not always, wrong.

He used, as an example, what he calls a “simple logic” question:

A smartphone and case, combined, cost £110. The phone costs £100 more than the case. How much is the case?

What is your answer?

Scroll down for the correct answer.

If you answered £10, like most people you are wrong.

The correct answer is £5.

Here’s how I figured it out:

If X is smart phone, and Y is the case.

X+Y = £110

X = £100+Y

£110 = £100+2Y

Therefore Y = £5 and X = £100+£5 = £105


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10 days ago

I got the right answer but went about solving the problem in a different way.
Let X= the price of the case and X+100= the cost of the phone.
X+X+100 = 110
2X = 110-100
2X = 10
X = 5

Jackie Puppet
Jackie Puppet (@jackie-puppet)
9 days ago

I got it right – I just did it in my head, like I almost always did basic math (or algebra) before I even knew what algebra was.

It’s kind of a gift for me, to do basic math quickly off the top of my head.

If I had to explain it how I arrived at my answer like they do in Common Core, I’d probably fail, cause I couldn’t explain it, it’s just something I know!

DCG (@dcg)
8 days ago
Reply to  Jackie Puppet

My mom is the same way when it comes to math. Y’all who can do it so fast are good!

I’ve always sucked at math…even had to have math tutors for chemistry because I seriously struggled. Hence I keep my calculator handy 🙂

TrailDust (@traildust)
3 days ago

Sorry folks, I got L10. Then again, algebra is my weakest area.