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

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

Make the seating arrangement of 10 children in such a way that there are 5 rows with 4 children in each row.

What work can one never finish?

Five thieves looted a bank and they ran away in a car. The bank staff informed the police and they began the search of their car in their jeep. They found them on a road and chased them eventually catching them. The light that is used to fill the number plate was broken on the thieves' car. Also, the headlights of the jeep police were not working. How were the police able to catch the thieves then?

Count the number of triangles in the given picture.

You can hear me, but you can't touch or see me.

What am I?

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?

On the dull night when the blonde was dozing, she heard an odd clamour and she saw that there was a bizarre man with a gun simply outside her home. So she raced to the telephone to call the police, however, she can't dial 911. Why?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?