Every minute there is 25 liters going in and 12 going out, so the bath is filling with 13 liters per minute.
Filling a 520 liter bath will take 40 minutes

364 (= 1 + 3 + 6 + 10 + 15 + 21 + 28 + 36 + 45 + 55 + 66 + 78)

Upside down they are the same

This is supposed to be a hard puzzle?

Or did you put it in the wrong category?
Or maybe adding a picture of a waterfall was a mistake?

Because that is the answer: a waterfall

250 days.
In general:
suppose there are N dwarfs with a red hat
a dwarf with a red hat will see N-1 dwarfs with a  red hat
a dwarf with a blue hat will see N dwarfs with a red hat
If at day N there are still dwarfs with a red hat and you see only N-1 dwarfs with a red hat his means you have a red hat and should not return the next day.

In a dictionary

There are 8 corners. Every corner is a join of 3 wires. Two of those can formed by bending a wire but the third one must be soldered.
So there need to be 8 solder connections.

To form the cube you need 4 wires. (No prove)

Because oct 31 = dec 25

For those who don’t understand the joke:
oct is an abbreviation of octal, and octal means a number with base 8.
oct 31 = 3*8 + 1 = 25

dec is an abbreviation of decimal, and decimal means a number with base 10.
This is the normal way to write numbers.
dec 25 = 2*10 + 5 = 25

You can try it out here: https://www.rapidtables.com/convert/number/octal-to-decimal.html

You only need two and they should NOT be placed at opposite sides.

At midnight one monk will kill himself.
If there were two or more monks with red eyes every one would have known there was at least one monk with red eyes.
This means there was only one monk with red eyes. Every other monk would know hat there was at least one monk with red eyes.
The monk with the red eyes only saw monks with brown eyes and never knew there was a monk with red eyes until the tourist told them.
He than knew he must be the one with the red eyes and killed himself.