With the help clues provided in the image, can you find the 5 digit key?

What does the below rebus riddle means?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

It belongs to you, but other people use it more than you do. What is it?

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.

On a bright sunny day, two fathers took their son fishing in the lake. Each man and son were able to catch one fish. When they returned to their camp, there were only three fishes in the basket. What happened?

PS: None of the fish were eaten, lost, or thrown back.

Yesterday I fell from 30 feet high ladder but I don't get hurt. Why?

What does this simple rebus mean?

1 dollar = 100 cent
= 10 cent x 10 cent
= 1/10 dollar x 1/10 dollar
= 1/100 dollar
= 1 cent

=> 1 dollar = 1 cent

solve this tricky problem?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99