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

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

what does the below math rebus puzzle mean?

'S' refers to the number of seconds in a day and 'H' refers to the number of hours in ten years. Which quantity out of these two is greater?

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

It has a long neck, A name of a bird, Feeds on cargo of ships, It's not alive,

What is it?

Find the last number in the series below:

voN luJ yaM raM ---

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?

Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?