What is common among 11, 69, and 88?

What's the only room from which no one can enter or leave

Two fathers and two sons decided to go to a shop and buy some sweets upon reaching. Each of them bought 1 kg of sweet. All of them returned home after some time and found out that they had 3kg of sweets with them.

They did not eat the sweets in the way, nor threw or lose anything. Then, how can this be possible?

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

What brings you down but never up?

A swan sits at the center of a perfectly circular lake. At an edge of the lake stands a ravenous monster waiting to devour the swan. The monster can not enter the water, but it will run around the circumference of the lake to try to catch the swan as soon as it reaches the shore. The monster moves at 4 times the speed of the swan, and it will always move in the direction along the shore that brings it closer to the swan the quickest. Both the swan and the the monster can change directions in an instant.
The swan knows that if it can reach the lake's shore without the monster right on top of it, it can instantly escape into the surrounding forest.

How can the swan successfully escape?

Can you find out what is missing?

1 3 5
2 4 ?

Hint: It's not six. Think out of the box.

Can you place three balls such that the equation shown in the picture holds true?

They are the five precious gems of an everyday sort and all can be found on a Tennis Court. Who are they?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?