What goes up but never comes down?

A man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.

Can you solve the below rebus?

I don't get anymore wetter, no matter how much rain falls on me.

There is a jar in which there are two types of candies.
20 blueberries and 16 strawberries. You perform the following steps:
1) You take out two candies.
2) If the two candies are of the same flavour, you add a blueberry one otherwise, you add the strawberry one.

You repeat these two steps till there is just one candy remaining in the jar. Which flavoured candy will be left?

To tease, King Akbar told his most clever advisor Birbal to give his daughter one thing that she can eat when hungry, drink if she feels thirsty and can burn if she feels cold. King Akbar was shocked when Birbal gave Akbar's daughter one such thing that satisfies all of the above.

What did Birbal give to Akbar's daughter?

How can you take 2 from 5 and leave 4?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

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

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