Here you can keep your brain fit by solving math related problems and also earn SBI by doing so.
The problems usually contain a mathematical equation that in my opinion is fun to solve or has an interesting solution.
I will also only choose problems that can be solved without additional tools, so don't grab your calculator, you won't need it.
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Rules

No upvote, No resteem, No follow required!

I will give 1 SBI to a random person who put a correct solution of the problem in a comment.

You have 48 hours to solve it.

In case there are multiple solutions, you have a higher chance of winning if you get all of them correctly.

Solutions can sometimes also be general like x = 20, y > -1. If there are multiple solutions submitted, that are part of the same general solution, they will be counted as one solution.

And one more thing: I only want integer solutions!

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Problem

The solution of this equation is simple, but it isn't as simple to get there.
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You can take a look at the results of the last contest here. There you can also find out how I evaluate your entries.

To everyone who already participated in a past contest, come back today and try a new problem(tell me if you don't want to be tagged):
@addax @ajayyy @bwar @contrabourdon @heraclio @hokkaido @mytechtrail @sidekickmatt @sparkesy43 @tonimontana @vote-transfer

In case no one gets a result(which I doubt), I will give away the 1 SBI to anyone who comments.

This contest is over. You can find the results here