Here's a useful tip that helps me sometimes:

When using ...Red / Black
Odds / Evens
High / Low

On average, when using these, the repeats outnumber the opposites by the ratio of 3:2.

Take red / black for example, you'll rarely ever get:

red/black/red/black/red/black/red/black/red/black/red/black/red etc

You usually end up with something like:

red,red,red,/black/black/red,red,red,/black,black,black,/red,/black,black etc

So, you get more repeats than you do opposites. That's why it makes more sense to bet on the repeats.

Monitor 100 spins and you'll see what I mean.

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