I’m bored of #fakemaths

We’ve all probably seen these posts on social media – little puzzles that all-but claim to be the hardest mathematical thing you’ll ever see, and after seeing another one I’ve had enough.


So this is going to be a guide for whoever is creates them: “How to keep post your little puzzle without it being #fakemaths”.

1)  Don’t head up the ‘problem’ with “only for genius”, “only expects can solve”, or similar – mainly because that is so very far from the truth. Maybe call it a number puzzle – after all, that is all it is.

2)  Don’t make claims about ~97% of people failing! There’s no such thing as failing at one of these (you’ve just not found the correct solution yet), and clearly that is a made up percentage.


3)  Type 1 puzzles – misuse of symbols, my pet peeve! Don’t take mathematical symbols that already have a set meaning and try to repurpose them (it’s either done because you’re trying to deceive or you don’t know any better, and neither is a good enough reason).
Using ⊕ is one option, although that still has its uses, the best solution would be to use function notation (no misuse there!):
f(5,8)= ?
You could then actually ask people then to describe what f(x,y) is!

4)  Type 2 puzzles – BIDMAS (like the one above). Orders of operations is not a trick, these are hardly puzzles in themselves, boring move on!


5)  Type 3 puzzles – simultaneous equations. Writing these things as a collection of silly pictures almost actively prevents people from simplifying the expressions and using maths to solve them. Plus most of the time the pictures have stupid subtle changes that are designed to trick the reader into using the wrong value – very boring!

6)  Type 4 puzzles – misusing percentages, especially when you’ve tried to assign each letter in the alphabet its own percentage from 1-26 (forgetting that 1-26 are not percentages, so the maths in the bottom half of above picture is complete rubbish to go with it:

Rant over. I’m sure there are more types… link me any more that you’ve found / been confronted by.


Calling the Maths Police

This afternoon Pizza Express engaged in some Twitter-based advertising that I feel warrants the attention of the #mathspoliceColin & Dave.

This looks to be a straight forward puzzle, but I expect the 140 characters limit has lead to the puzzle being set without enough rigour, or was it just another example of a pizza chain and it’s careless approach to maths? As I see it, there are at least 2 different interpretations to the question provided.

1) Those 2 people order 2 pizzas in 2 minutes, therefore their rate of ordering is 1 pizza/minute. So if they continue to order more pizzas at that rate them alone will order all 500 in 500 minutes (i.e. the answer is 2 people).

2) If the restaurant is full of people and everyone orders just one pizza (not mentioned in the question so would have to be a heavy assumption) and everyone we consider orders at the same rate as the original couple then it will take 500 people (if they’re ordering in series).

3) Anyone have any other interpretation?

As it stands I believe that #1 is the most accurate answer, regardless of how greedy it makes those 2 look. It comes down to the question referring to the rate at which the couple is ordering their pizzas at: they are ordering at a rate of 1 pizza per minute so just the 2 of them will order the full quota in the desired time.

Pizza Express have chosen the second option, which I feel only works as an answer if the question is rephrased. They can blame 140 characters, but I blame bad maths… #mathspolice I turn the investigation over to you.

Fair coin puzzle

^^ Not the most complicated maths in the world, but it forsure solves the problem 😀

What's on my blackboard?

FairCoinPuzzleThis board was sent to me via Twitter by Will Davies (aka @notonlyahatrack) who had listened to the podcast Wrong, But Useful (by Colin Beveridge (@icecolbeveridge) and Dave Gale (@reflectivemaths) ) and attempted the following puzzle:

I have three indistinguishable coins: one always comes up heads, one always comes up tails and the third is a fair coin. I pick one of the coins at random and toss it twice and get the same result both times. What is the probability I picked the fair coin?

You should have a go at the puzzle yourself before looking too closely at the solution in the photo!

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