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Three Immovable Pentablocks

Today I’m sharing the Three Immovable Pentablocks Puzzle with you.

This summer, I’m on a mission to make as many puzzles as possible for my classroom from a bag of 100 wooden cubes that I purchased from Amazon.

So far, I have used 6 of these wooden cubes to make a set of Genius Blocks and 27 of the blocks to create a SOMA Cube. 33 blocks down – only 67 more to go!

Genius Blocks

Project #3 uses 15 more of these blocks to form a puzzle called “Three Immovable Pentablocks.”

Three Immovable Pentablocks Puzzle

The goal of the three immovable pentablocks puzzle is to place the three pentablocks within a 7 x 7 tray so that it is not possible to slide any of the pieces in any direction.

This puzzle is from The Big, Big, Big Book of Brainteasers by The Grabarchuk Family. It’s out of print which makes the used copies on Amazon a bit pricier sometimes than I would prefer. If you can pick up a used copy for a good price, DO IT! This is one of my favorite puzzle books. It has such a variety of different puzzles and SO many of them!

You can still access quite a few of the puzzles for free, though. Amazon’s Look Inside Feature
allows you to look at quite a few of the puzzles in The Big, Big, Big Book of Brainteasers for free. Just keep clicking “Surprise Me!” on the left pane to see a different page of puzzles.

I began my project by joining my one-inch wooden cubes with wood glue to form the five puzzle pieces.

Three Immovable Pentablocks Puzzle

I don’t own any clamps to properly hold the blocks together while they are drying, so I once again turned to my trusty hair bands to do the job for me!

Three Immovable Pentablocks Puzzle

Once the glue was dry, I had to figure out how to make a tray to place the puzzle pieces in.

Three Immovable Pentablocks Puzzle

Since my blocks are one-inch cubes, I created a 7 x 7 table where each cell was a one-inch square to correspond with the blocks.

I cut slits from each corner of the paper to each corner of the grid.

Three Immovable Pentablocks Puzzle

With these slits cut, I started folding up the sides of the paper along the edge of the grid. 

Three Immovable Pentablocks Puzzle

Once all the sides were folded up, I folded the small triangles over so the sides could be easily glued together.

Here’s what a corner looks like once it’s been glued.

Three Immovable Pentablocks Puzzle

Now, it’s starting to actually look like a tray!

Three Immovable Pentablocks Puzzle

To make the tray sturdier (and hopefully stand up to the abuse of teenagers!), I started cutting pieces of cardstock to glue around the sides of my paper tray.

I folded each piece of cardstock in half.

Three Immovable Pentablocks Puzzle

Then, I folded one of the halves in half again.

Three Immovable Pentablocks Puzzle

These folds make the cardstock fit exactly over the side of the tray with a large overlap on the bottom of the tray to make it sturdier.

Here’s what the bottom looks like after gluing on the cardstock:

Three Immovable Pentablocks Puzzle

Now, repeat this process three more times.

I glued an extra scrap of cardstock on the bottom of the tray to finish it off.

A finished tray for my three immovable pentablocks puzzle! It’s not absolutely perfect because one of my sides ended up slightly taller than the other three, but I’m still really proud of it.

Three Immovable Pentablocks Puzzle

At this point, I decided it was time to actually attempt to solve the three immovable pentablocks puzzle. Remember, the goal of the puzzle is to place the three pieces in such a way that none of them can move within the tray.

That’s when I discovered that this puzzle is VERY tricky. After trying arrangement after arrangement, I took a break. My husband, of course, came over and solved the puzzle in just a minute or so as I kept my eyes closed so the puzzle wouldn’t be spoiled.

Once I knew that the three immovable pentablocks puzzle could indeed be solved, I went at the puzzle with a new vengeance. (Of course, I never actually doubted that the puzzle could be solved. It did come from a published puzzle book, after all…)

One thing that I found frustrating in my attempts at this puzzle was that it was sometimes hard to tell where one puzzle piece stopped and the next began.

I got out my newly purchased collection of Apple Barrel paint and several paper plates and got to work to fix this issue.

It worked! The puzzle pieces are now easy to distinguish from one another.

I was pretty excited when I figured out how to make the pieces fit all the way across the grid – until I realized that the entire column of pieces could be slid across the tray.

Three Immovable Pentablocks Puzzle

I won’t spoil the three immovable pentablocks puzzle for you, but I will reassure you that it can be solved! There’s great satisfaction to be had from shaking the tray and watching the puzzle pieces that you created stay in place!

Three Immovable Pentablocks Puzzle

Free Download of Three Immovable Pentablocks Puzzle

Want to create a copy of the three immovable pentablocks puzzle for your own classroom?

3 Immovable Pentablocks (PDF) (917 downloads )

3 Immovable Pentablocks (Editable Publisher File ZIP) (750 downloads )

Puzzle Solutions

I intentionally do not make answers to the printable math puzzles I share on my blog available online because I strive to provide learning experiences for my students that are non-google-able. I would like other teachers to be able to use these puzzles in their classrooms as well without the solutions being easily found on the Internet.

However, I do recognize that us teachers are busy people and sometimes need to quickly reference an answer key to see if a student has solved a puzzle correctly or to see if they have interpreted the instructions properly.

If you are a teacher who is using these puzzles in your classroom, please send me an email at with information about what you teach and where you teach. I will be happy to forward an answer key to you.

More Wooden Block Puzzles


Monday 5th of August 2019

I bought 1/2 inch blocks instead of 1"! Maybe I can shrink the tray by 50% :-)

Sarah Carter (@mathequalslove)

Tuesday 6th of August 2019

That should work!

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