This puzzle is for Harry Potter fans. Do you know why Tom Riddle is called Lord Voldemort?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

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

If you go to the movies and you're paying, is it cheaper to take one friend to the movies twice, or two friends to the movies at the same time?

I’m tall when I’m young, and I’m short when I’m old. What am I?

If Rajina's daughter is my daughter's mom, who am I to Rajina?

I throw two dice simultaneously.

What is the probability of getting a sum as 9 of the two numbers shown?

Your last good ping-pong ball fell into a narrow metal pipe embedded one foot deep in concrete.
How can you get it out undamaged, if all the tools you have are your tennis paddle, shoe laces, and plastic water bottle, which does not fit into the pipe?

The Puzzle: A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.
How far does the dog travel in 1 hour?

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?