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(at least not if you can calculate basic stuff in your head), so don't grab your calculator, you won't need it.
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Every friday and tuesday!

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Rules

No upvote, No resteem, No follow required!

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

You have 48 hours to solve it.

Some additional rules for the case that the problem is an equation or a collection of equations.

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: If there are infinitely many solutions, I only want integer solutions!

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Problem

I decided for a problem with trivial solutions again:

+1 SBI for a random person who can (roughly) plot the solutions!
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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 @athunderstruck @bwar @contrabourdon @golddeck @heraclio @hokkaido @iampolite @masoom @mmunited @mytechtrail @onecent @sidekickmatt @sparkesy43 @syalla @tonimontana @vote-transfer @zuerich

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

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@contrabourdon sponsors this contest with 2 STEEM weekly.
You can support him by using a witness vote on untersatz, so he can further support this and other contests.