Explain why manhole covers are round. Why is this design better than, say, a square design.

You want to check that your friend, Bill, has your accurate phone number, but you can't ask him directly. You have to write a question on a card which and give it to Ava. She will take the card to Bill and then return the answer to you.

What should you write on the card to ensure Bill can encode the message so that Ava cannot read your phone number?

You have a closet with 300 shirts in it. Consequently, you find it hard to find a shirt quickly while dressing for work in the morning.

What can you do to organize your shirts to minimize the time that it takes to find the correct one?

Imagine you have eight balls, each of the same size.

One of the balls weights slightly more than the other seven.

Using a balance, find the heavier ball using only two weighings.