I am reminded of a talk I attended in college about (elementary-level) math education. One of the first intro problems to estimation was something like 27+75, and the presenter showed us a (real) dialogue where the student gave the exact answer, and the teacher had to "correct" them to the estimate, and then proceeded to talk about how this wasn't exactly correct. The teacher's guiding the student through the "proper" reasoning was convoluted, and not effective teaching. The presenter concluded that if you teach estimation, you should use an example like 209385324579+394875293745, where estimation is actually faster and easier than exact arithmetic.<p>Now, what real-life example demands systems of equations? I suspect none, until you get into industrial applications. Therefore, maybe you should ask what the kid wants to be when he grows up, and create an example in that setting.