Here are two puzzles about finding fake coins among real ones, by weighing them.

"Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.”
― Kenneth Grahame, The Wind in the Willows

Here are three classic River Puzzles, which require you to get a group of people, things and whatnot from one side of a river to the other, by sending a rowing boat back and forth several times. There are lots of these about, but the three presented here are good examples of the genre.

There are quite a few methods for multiplying large numbers together. Watch this video to learn about Long Multiplication and how it compares to some of the others. Then download the software to get practising.

Chunking video and software

Don't be put off by the name - it might not sound as serious as Long Division, but it's a very effective method.

If you already know Long Division, seeing Chunking might give you a feeling of smug superiority. Yet Chunking is a far more friendly method for learning about dividing, and not nearly as poor a relation to Long Division as some would have you believe.

In the BigSoftEd video on Long Multiplication, the odd "Russian Peasant" method is seen, but not heard. It might seem to be the odd one out but, watch this video to find out what it's all about, why it works, and how it's connected to those other methods after all.