When can we add 2 to 11 and get 1 as the correct answer?

There are three boxes of different sizes with three cupcakes inside each of the boxes in Christina's kitchen. At night her daughter wakes up and goes to the kitchen. She opens a box and eats all three cakes.

But in the morning Christina finds out that each box still had three cupcakes. How?

Replace the question mark with the number below given a simple math problem.

Find three whole, positive numbers that have the same answer when multiplied together as when added together.

Spot 5 differences in two Christmas tree below:

How many triangles can you count in the figure given?

Below toothpicks/matchsticks indicate the group of fishes moving from west to east direction. Can you make them move from east to west by just moving three toothpicks/matchsticks?

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.

What has lots of eyes, but can’t see?

What is so fragile that saying its name breaks it?