What has no start, end, or centre?

After teaching his class all about Roman numerals (X = 10, IX=9 and so on) the teacher asked his class to draw a single continuous line and turn IX into 6. The teacher's only stipulation was that the pen could not be lifted from the paper until the line was complete.

You can hear me, but you can't touch or see me.

What am I?

I make a loud sound when I’m changing. When I do change, I get bigger but weigh less. What am I?

Find the next number in the sequence

5 12 24 36 ?

Paul's height is six feet, he's an assistant at a butcher's shop and wears size 9 shoes. What does he weigh?

If you read clockwise, you can form a word by inserting three missing letters in the picture given below. Can you do it?

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

A boy and a girl are sitting on the porch.
"I'm a boy," says the child with black hair.
"I'm a girl," says the child with red hair.
If at least one of them is lying, who is which?

Count the number of times the letter "F" appears in the following paragraph:

FAY FRIED FIFTY POUNDS OF
SALTED FISH AND THREE POUNDS
OF DRY FENNEL FOR DINNER FOR
FORTY MEMBERS OF HER FATHER'S FAMILY.