In how many ways can you make it up the stairs?

Making a very special number out of primes.

A life insurance agent knocks on a door. A woman answers and he tries to sell her a policy. He asks her how many children she has and their ages. She replies: "I have three children, but I will not even listen to your sales pitch unless you guess their ages..."

Find the number x that satisfies two interesting properties.

A mad robot sets off on a journey mindlessly following a set of instructions. Where will it explode?

Sharpen that wooden stake!

Which gives a tighter fit: a square peg in a round hole or a round peg in a square hole?