Replace the question mark with the correct number below.

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

Why do you find that most of the buildings are deprived of the 13th floor?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

The day before yesterday I was 25 and the next year I will be 28. This is true only one day in a year. What day is my birthday?

John said, "If yesterday was tomorrow, today would be Friday."

When did John make this statement?

What happened when the wheel was invented?

You are mixing a mixture of cement and Sand with five gallons of water. You have a garden hose giving you all the water you need. The problem is that you only have a four-gallon bucket and a seven-gallon bucket and neither has graduation marks. Find a method to measure five gallons.