Sort:  

1/ Let's do the math then.

Already 22 days passed. The 50th spot is enjoying 19362 XP, let's round it off to 20k XP. In 22 days 20k XP, another 22 days, another 20k XP.

2/ But as the competition has gone up, we need to add a certain additional weight in the final days of the sprint. So let's add 1.5 times into the final 22 days. That will be 30k XP, so I think 50k XP will be safe to remain in the top 50.

50 for 50. well 50k seems reasonable & I should be able to do that. Did they ever say what the prizes are, and how deep the pool is?

Did they ever say what the prizes are, and how deep the pool is?

No that's still a mystery. But I guess the top 20 will have a decent reward. The remaining might get a consolation reward.