Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209

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

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

Can you convert the number zero(0) into a positive number using just one mathematical operator ?

When we see 2 but call 10?

A sundial has the fewest moving parts of any timepiece. Which has the most?

How many triangles are there on the puzzle below?

I inserted a coin in a bottle and closed its mouth with the help of a cork. Now, I was able to take the coin out from the bottle without taking out the cork or breaking the bottle. Can you tell me how I did it?

If two's company, and three's a crowd, then whats four and five ?

How many times can you subtract the number 5 from 25?