What occurs twice in a week, once in a year but never in a day?

Can you find out who is the kidnapper in below Picture and why, Explain ?

Can you make four (4) nines (9) equal 100?

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.

Count the squares in the matchstick puzzle below?

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?

In the Mexico City area, there are two Houses H1 and H2. Both H1 and H2 have two children each.
In House H1, The boy plays for Mexico Youth academy and the other child plays baseball.
In House H2, The boy Plays soccer for his school in Mexico and they recently have a newborn.

Can you prove that the probability of House-H1 having a girl child is more than that of House-H2?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

Solve this riddle by finding the odd one out from the rest.

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?