What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

How many letters are in the alphabet?

Through your logical capabilities, can you make 7 an even?

Can you replace the question mark with the correct number?

When you stop to look, you can always see me. But if you try to touch me, you can never feel me. Although you walk towards me, I remain the same distance from you. What am I?

O_er_t_o_

Complete the missing letters of the given word.

Can you find out the missing number?

? 4 5 3 5

9 5 7 10 3

What does it mean?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not rounded numerals equals 24.

John and Jenni are a married couple. They have two kids, one of them is a girl. Assume safely that the probability of each gender is 1/2.
What is the probability that the other kid is also a girl?

Hint: It is not 1/2 as you would first think.