What is common among 11, 69, and 88?

What is the next number in the series?

15 29 56 108 208 ?

Which three-digit number, made of consecutive digits, like 567, is 2 less than a cube and 2 more than a square?

How many words can a pen with half refill write?

Solve the equation in the image by looking at the pattern closely.

A man lives on the fifteenth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator, or if it was raining that day, he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up five flights of stairs to his apartment. Can you explain why he does this?

The captain of a ship was telling this interesting story: "We travelled the sea far and wide. At one time, two of my sailors were standing on opposite sides of the ship. One was looking west and the other one east. And at the same time, they could see each other clearly." How can that be possible?

Can you count the number of triangles inside a triangle?

Solve the alphametic puzzle by replacing the alphabet with the number.

S T O R M +
S O L E S
=========
T O W E L
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What is the relationship between these matchstick pictures below?