I have been having some success with my learners around open ended up problem solving tasks.
Rather than coming up with all the problems myself, I have been coming up with open ended problems that the learners make up themselves. I had feared that the learners wouldn't take this seriously and it would be a waste of time.
However, they instead rose to the challenge and were excited about difficult problems, rather than rigging it to get easy ones like I thought.
To make sure that they were solving the problems correctly I encouraged them to use the calculator on their chromebooks. There was no threat to their learning as they were still required to show their working, which was not made easier by having the answer.
You can see two of the tasks I created on my Class OnAir page. Other problems were designed from using materials.