Why is the Hole below a Lock?

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

What is the Surname of Barbie Doll?

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?

What is always in front of you but can’t be seen?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Three ants are sitting at the three corners of an equilateral triangle. Each ant starts randomly picks a direction and starts to move along the edge of the triangle. What is the probability that none of the ants collide?

What comes
Once in a Year
Twice in a Month
4 times in a Week
6 times in a Day

One is to three as three is to five and five is to four and four is the magic number.
What is the pattern?

What does below chemistry rebus means?