I am an odd number. Take away a letter and I become even. What number am I?

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

How many triangles are there in the picture below?

Krish is 45 years old and his mother Crishtina is 73 years old.

Can you find out how many years ago, his mother was three times his age?

Solve below popular number sequence
314 159 265 358 979 323 846 ?

Using Only Five 5's and any mathematical operator make sum as 37

There is a hypothetical state between the USA and Mexico border 'Tango'.
Here 70 percent of the population have defective eyesight, 75 percent are hard of hearing, 80 percent have Nose trouble and 85 percent suffer from allergies, what percentage (at a minimum) suffer from all four ailments?

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