Can Two 2’s Produce 5?

numbers

Using only two 2’s and any mathematical operations, functions and symbols that you want (and I mean ANY!), try to make two 2’s equal to 5. Trust me, this problem is harder than it looks as you would find out if you choose to solve this problem. So, if you really want a difficult challenge, then try to solve this first before looking at the solution.

Solution

When a friend of mine gave this problem to me , I thought that it’s not even that challenging. I was very surprised at the level of difficulty of this deceptively simple-looking problem. Through several trials and errors and probably dumb luck, I eventually solved it but I felt very dizzy afterwards.

Now, here’s the solution,

\sqrt{.2^{-2}}, which is equal to \sqrt{25}=5

Note that .2^{-2}=\frac{1}{(.2)^2}=\frac{1}{.004}=25

As you can see, the solution involved a decimal, a square root, an exponent and a negative number! If you also found this solution by yourself, then I’d like to congratulate you.

In hindsight, it’s pretty easy to find another solution. Admittedly, though, it’s almost the same as the first solution:

(\sqrt{.2})^{-2}=\frac{1}{\sqrt{.2^{2}}}=\frac{1}{.2}=5

About Edmark M. Law

My name Edmark M. Law. I work as a freelance writer, mainly writing about science and mathematics. I am an ardent hobbyist. I like to read, solve puzzles, play chess, make origami and play basketball. In addition, I dabble in magic, particularly card magic and other sleight-of-hand type magic. I live in Hong Kong. I blog at learnfunfacts.com. You can find me on Twitter @EdmarkMLaw and Facebook. My email is learnfunfacts@gmail.com
This entry was posted in Mathematics, Puzzles and tagged , , , . Bookmark the permalink.

15 Responses to Can Two 2’s Produce 5?

  1. From E. E. Cummings’ prelude to his book, entitled “is 5″ :

    On the assumption that my technique is either complicated or original or both, the publishers have politely requested me to write an introduction to this book.
    At least my theory of technique, if I have one, is very far from original; nor is it complicated.
    I can express it in fifteen words, by quoting The Eternal Question And Immortal Answer of burlesk, viz.”Would you hit a woman with a child? – No, I’d hit her with a brick.” Like the burlesk comedian,
    I am abnormally fond of that precision which creates movement.
    If a poet is anybody, he is somebody to whom things made matter very little–somebody who
    is obsessed by Making. Like all obsessions, the Making obsession has disadvantages; for instance, my only interest in making money would be to make it. Fortunately, however, I should prefer to make almost anything else, including locomotives and roses.It is with roses and locomotives (not to mention acrobats Spring electricity Coney Island the 4th of July the eyes of mice and Niagara Falls) that my
    “poems” are competing.
    They are also competing with each other, with elephants, and with El Greco.
    Ineluctable preoccupation with The Verb gives a poet one priceless advantage: whereas
    nonmakers must content themselves with the merely undeniable fact that two times two is four, he rejoices in a purely irresistible truth (to be found, in abbreviated costume, upon the title page of the present volume).

    Liked by 2 people

  2. Excellent problem. I took a long while, but never quite got there!

    Liked by 1 person

  3. Bunk Strutts says:

    Assume that we’re talking about parents and offspring. The first couple (2a) has twins, the second couple (2b) has triplets. Combining the number of offspring between them, 2a + 2b = 5.

    Liked by 1 person

  4. I like this one. It makes sense.

    Liked by 1 person

  5. I had always heard that an accountant can make the numbers mean what you want them to mean.

    To the point that in a spreadsheet, was the category MSP Meaning: . money some place

    Liked by 1 person

  6. Pingback: Can Eight 8’s Produce 1000? | Learn Fun Facts

  7. This was an interesting challenge 🙂 I found a more simple solution that also comes to the same result: 2×2+2/(2×2)×2=5

    Liked by 1 person

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s