Find the next number in the sequence

1, 2, 6, 21, 88, __?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not rounded numerals equals 24.

Teacher ask the student

'Why are you standing on that chair in music class ?'.

what did student replied ?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

Can you find the thief by just looking at the picture below?

Below, you can see three complete equations and one incomplete. Based on the three complete ones, can you complete the incomplete one?

5 $ 4 $ 3 $ 9 = 4215
6 $ 9 $ 2 $ 6 = 3816
4 $ 7 $ 3 $ 3 = 1122
7 $ 2 $ 7 $ 4 = ____

If we tell you that there is a relation between the numbers and letters in the given figure, can you analyze it and find the missing letter in the last box?

Can you count the number of lines in the below picture?

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

There are five vowels (a, e, i, o, u) in the English language.
Can you tell us a word that contains all these vowels?