Okay, you're not actually going to pour any water, so don't worry about getting your classroom soaked (or your kids.....)
This is a re-visiting of a very old math problem, which involves using 3 cups: one is 8 ounces, another holds 5 ounces and another holds 3 ounces. You fill up the 8 ounce cup to the top, and by pouring water back and forth, end up with 4 ounces in 2 cups. Sounds easy? Well, maybe, but it will take 7 steps to do it, and for a lot of your kids, doing a 2 step problem may be challenging.
This is a cool problem to use, because it uses actual mathematical skills (addition and subtraction combinations) and leads to a nice solution. Oh, and there is a beautiful pattern which emerges from the solution which can be applied to an even harder problem, which I've helpfully supplied: that problem, which is just slightly trickier version, uses 11 steps.
Now, you're probably saying, why is this for 3rd graders "and up" if this is such a dastardly tricky problem? Because the math skills are easy: if you can add three numbers to make 8, then you can definitely work on this problem. This is great, because the computations are simple, but it's keeping track of all the steps as you go back and forth that are more complex (think "executive processing....")
And yes, there is an answer key, so you don't have to figure out all 11 steps if you're in a hurry. I've also included some tips on how to look at the patterns in the solution and apply it to much more difficult problems. Oh, and there's much, much more to do!