Combinations

You have two egg timers. One takes 4 minutes exactly to empty and the other takes 7 minutes. What times in whole minutes can you measure and how?

My briefcase has a three-number combination lock, but I have forgotten the combination. I remember that there's a 3, a 5 and an 8. How many possible combinations are there to try?

Here are the prices for 1st and 2nd class mail within the UK. You have an unlimited number of each of these stamps. Which stamps would you need to post a parcel weighing 825g?

The machine I use to produce Braille messages is faulty and one of the pins that makes a raised dot is not working. I typed a short message in Braille. Can you work out what it really says?

Terry and Ali are playing a game with three balls. Is it fair that Terry wins when the middle ball is red?

What is the smallest number of ferry trips that Neda needs to take to visit all four islands and return to the mainland?

How many ways can you find of tiling the square patio, using square tiles of different sizes?

Use the clues to work out which cities Mohamed, Sheng, Tanya and Bharat live in.

Using all ten cards from 0 to 9, rearrange them to make five prime numbers. Can you find any other ways of doing it?

In this challenge, buckets come in five different sizes. If you choose some buckets, can you investigate the different ways in which they can be filled?