Transform the word THINK into BRAIN while changing only one letter at a time in a manner that each of the word in the process is a real word!!!

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

Can you Find and name the hidden bird in the picture below ?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?

Replace the question mark with the correct number in below Picture:

Identify The phrase in the picture.

In one of the popular batman series movie "Batman Forever", there was a riddle that goes like "Tear me off and then scratch my head and I was red then and now I am back. Who am I?

Replace the question mark with the correct number.

2 + 2= 4
3 + 3= 18
4 + 4= 48
5 + 5= ?

Take away the whole and some still remain. What is it?

Solve the following series:
AZ, GT, MN, __, YB