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If $a$ and $b$ are positive integers for which $ab - 3a + 4b = 131$, what is the minimal possible value of $|a - b|$?

 Aug 14, 2024
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Ok, so we start off with the equation

ab3a+4b=131

 

I know this is random, but let'st ake the product of the coefficients on a,b.....add this product to  both sides

So this gets us

ab3a+4b+(43)=131+(43)ab3a+4b12=119

 

This eventually achieves the equation

(a+4)(b3)=119

 

Now, the factors of 119 are 1,17,119

Since we want the minimum, let's use 7 and 17. We have

(13+4)(103)|ab|=|1310|=3

 

Thus, our final answer is 3. 

 

Thanks! :)

 Aug 14, 2024
edited by NotThatSmart  Aug 14, 2024

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