What is common among 11, 69, and 88?

Can you count the number of triangles in the given picture?

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?

Can you name four days which start with the letter 'T'?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

What work can one never finish?

I have nine bottles of wine and one of the nine bottles is poisoned.
I need to find the poisoned bottle with two facts
(1) Poison is deadly, only a sip will cost death
(2) I have two mice to do so.

How should I do it?

An equation has been laid down using a few matchsticks. However, as you can see, the equation is not correct. Can you correct the equation if you are allowed to add or remove 5 matchsticks?

What is the next number in the series?

15 29 56 108 208 ?

At a party, there are five people and a whole round cake lying at the centre of the table. Only four people will make a cut and take their piece and the last one will get the remaining piece on the table. How can they make sure that everyone gets a 1/5th of the piece?