What question can you never answer yes to?

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

No matter how little or how much you use me, you change me every month. What am I?

Can you count the number of triangles in the given picture?

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

Two guards were guarding the camp.Guard-1 was looking towards the south to make sure no threat is coming from the road.Guard-2 was looking at the north to make sure no threat is coming from the top. Suddenly Guard-1 ask the Guard-2 why he is smiling?How Guard-1 knows that Guard-2 is smiling?

Find The Missing Number In the Sequence.
6 25 64 ? 32 1

Three brothers Jacob, John, and James live in Mexico City. The product of the ages of these brothers is 175. Jacob and John are twins. How old is James?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

Can you quickly find which two matchstick figures are identical?