Can you find the least possible number such that

If the number is divided by 3, it gives the remainder of 1;
If the number is divided by 4, it gives the remainder of 2;
If the number is divided by 5, it gives the remainder of 3;
If the number is divided by 6, it gives the remainder of 4.

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

We know that the number 7 is the prime followed by a cube. Which next number is also a prime followed by a cube?

What is next number in the pattern below:

131 517 192 123 ?

Which three-digit number, made of consecutive digits, like 567, is 2 less than a cube and 2 more than a square?

Find out a multi-digit number that if multiplied by the number 9 or any of its multiplications products (i.e. 18, 27, 36, 45,..) will result in the multiplication factor repeated (n) number of times.

Can you write down eight eights so that they add up to one thousand?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10