100-sided dice was rolled 98 times, Numbers form 1 to 50 were rolled exactly once, except number 25, which wasn't rolled yet. Number 75 was rolled 49 times You can only bet if the next roll result will be below 51 or above 49.
How do you choose ?, how to calculate which bet is better ? ELI5 please
And would it be more reasonable to chose below 51, if 75 was rolled only 48 times ?
EDIT: yes dice is fair EDIT sorry, below 51 or above 49.
If the die is fair, then the probability the roll will be above $51$ is $49/100$ and the probability the roll is below $49$ will be $48/100$. The previous rolls do not change the fact that the die is fair. So technically, since it's slightly more likely, you should bet that the roll is above $51$.
If you do not assume the die is fair, and you know nothing about the die beforehand, then the maximum likelihood estimate for what you should choose would be whichever is greater, the number of rolls less than $49$ or the number of rolls greater than $51$. If you have prior knowledge about how the die might behave, then you can use Bayes rule (you can look it up online) to figure out what to do but the calculations get messier.
UPDATE: The question has been changed to "below 51" or "above 49". If the die is fair, then "below 51" has chances $50/100$, and the chances of "above 49" are $51/100$, so you should choose "above 49" if the die is known to be fair. All the other reasoning stands as is (for a possibly unfair die), just substituting in the new different things you bet on.