How many ordered pairs [tex](b,y)[/tex] of positive integers with [tex]4 \le b \le y \le 2007[/tex] are there such that when [tex]b[/tex] blue balls and [tex]y[/tex] yellow balls are randomnly arranged in a row, the probability that the balls on each end have the same colour is [tex]1/2[/tex]?(adsbygoogle = window.adsbygoogle || []).push({});

PS: Is there a button such that I could just click on it after I highlighted the text that I want to be included in the LaTeX tags? It's going to save me a lot of typing if there's such button (without keep typing [tex] and so on)!

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# Tough (algebraic) probability problem.

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