Change Four Dots To Make This True! Most People Fail

Thanks to Professor Peer Johannsen at Pforzheim University for creating this puzzle! Color four dots blue or erase four blue dots to make a valid equation: (10 + 11)(10 - 11) = 100 + 1! Watch the video for the amazing answer!

The 71 Puzzle - One Dot Changes Everything!

Playlist to watch all videos on MindYourDecisions

This is the only channel to feature math topics suggested by people around the world. Support the channel on Patreon so we can share the beauty of mathematics and make the world a better place:

If you buy from the links below I may receive a commission for sales. This has no effect on the price for you.

My Books
"The Joy of Game Theory" shows how you can use math to out-think your competition. (rated 3.9/5 stars on 35 reviews)

"The Irrationality Illusion: How To Make Smart Decisions And Overcome Bias" is a handbook that explains the many ways we are biased about decision-making and offers techniques to make smart decisions. (rated 4.6/5 stars on 3 reviews)

"Math Puzzles Volume 1" features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.4/5 stars on 13 reviews.

"Math Puzzles Volume 2" is a sequel book with more great problems. (rated 4.5/5 stars on 6 reviews)

"Math Puzzles Volume 3" is the third in the series. (rated 4/5 stars on 6 reviews)

"40 Paradoxes in Logic, Probability, and Game Theory" contains thought-provoking and counter-intuitive results. (rated 4.4/5 stars on 13 reviews)

"The Best Mental Math Tricks" teaches how you can look like a math genius by solving problems in your head (rated 4.8/5 stars on 5 reviews)

"Multiply Numbers By Drawing Lines" This book is a reference guide for my video that has over 1 million views on a geometric method to multiply numbers. (rated 4.4/5 stars on 5 reviews)

Connect with me

[MindYourDecisions]

At MindYourDecisions we always keep it 💯. Are there any other solutions? (And to set the record straight: (10 + 1!)(10 - 1!) = 100 - 1! is not a solution: I specifically designed the puzzle to exclude that! Notice the subtraction - symbol has 4 horizontal dots while the addition + symbol has 3 horizontal dots. So you would need to change 3 dots to make + into a - (erase 2 dots and then add 1 more dot. This is problematic since you have to either add 4 dots OR erase 4 dots, not add some and erase others. Plus the diagram does not have room to even add a dot next to the plus, it would then connect with the 0 from 100 or the 1 from 1!). I am surprised more people are not noticing these details! It is a close answer though :)

[NestorAbad]

I did: (10+1!)(10-1!)=100-1!, so I removed one dot for each 11 to make 1!, and two more dots in the rightmost + to make it a -.

[crazygoat]

Take 1 dot from both elevens to make it a '1!'
2 dots then are removed from the last plus sign to make it a minus.
(10+1!)(10-1!)=100-1!

[MotesTheMathNotes]

Call me crazy, but I think I came up with a rather unique solution.
A minus sign, as depicted above, consists of four dots.
Add four dots to the front of the left-hand side of the equation.
-(10+11)(10-11)=100+1!
_Now read this in binary_
5=5 Woot

[KlokJammer]

Erase four dots to make (10 + 1!)(10 - 1!) = 100 - 1! which simplifies to 99 = 99. But I'm 100% sure you knew that and are just trying to show off by using a complex solution with complex numbers.

[mittfh]

"The solution is *complex* but the answer is quite *real* !"
Oh dear, mathematical punnage!

[johnchessant]

Instead of reading the "+" as plus, read it as "÷" instead. Then add four dots to make: "(10 ÷ 1!)(10 ÷ 1!) = 100 ÷ 1!". Voilà!

(Yes, I know the second "÷" and the first two factorials would be very unbalanced, but it's the best new solution I can find.)

[ghabhitho]

it is a good one, but we could also make it into (10+1!)(10-1!)=100-1!=99

[urisadan-yarchi]

You can also turn each eleven to 1! And the minus at the other part of the equation to plus.

[fizixx]

If you edited the "i" differently you could argue that this can be done by altering only 2 dots.
Instead of erasing the top dot and the third dot, just erase the second dot for the 2 i's.
It's no different other than the i's are one dot taller.
Thank u for the video Mr. Talwalkar

[SomeGuyx]

I figured it out within a minute. Remove the second dot from the bottom of the right "1" in the first two "11"s, to turn them into "1!"s. Then, remove the top and bottom dots from the "+" at the end, to turn it into a "-". This results in:
(10+1!)(10-1!)=100-1! ...which is... 11 x 9 = 99.
EDIT: Watching the rest of the video... Oh, I didn't think of going for imaginary numbers.

[Robin-kcm]

(10+1!)(10-1!)=100-1! is another solution.

[khushalkaakran]

I did(10+1!)(10-1!)=100-1! is it also true or not reply Presh bro

[elton]

this problem was too complex for me

i get to say this because of your joke at 2:16

[parkamark]

Didn't see the "i" solution at all. But I was going to use 4 dots to place a strike through on the equal sign (≠), which would have then made the equation valid. ;-)

[shivaargula]

You got me the last time you showed the "blue dots" puzzle, but the same trick doesn't work twice. This one is so much more blatantly obvious, too. Once you know that 1 can be turned into a factorial, it becomes insanely simple to figure out.

[rafaelrossisilveira]

It's almost already correct if you read module instead of 10+11, read module of zero plus one, etc. Just add a dot to the last module

[marcoperndrecaj]

You can make each 11 to become 1!, so you have 11×9 on the left, and then you remove the two dots to make the + become a - on the right side. So you have 11×9=100-1!, but the only problem is that you made the - have 4 dots, while on the right side you would have a 3 dot -.

[JBaker]

Seriously Presh, how much time are we expected to spend on these type of problems ;-)

[pulsehead]

“The answer is real”

I disagree. Once i entered the equation things became imaginary.