"Systems of equations" covers a lot of ground. Almost all math problems in engineering (of all kinds), physics (from subatomic particles to the nature of the universe), and finance (of all kinds) involve systems of equations. Many have to be simplified to 2 or a few variables in order to make them workable. The word problems in your text are examples of real-world situations that can be modeled by systems of equations. (Some are more realistic than others.)
Word problems will typically involve mixtures (how much of each do I need to get a particular mix?), time and distance (when will travelers meet?), profit and loss (at what point do costs match revenue?), resource utilization (how long will supplies last?; what is the benefit of working together?; what can I build with the resources I have?).
Here are a couple of specific examples.
1) Two solutions are available: 1% solution and 5% solution. In what proportion must they be mixed to get a 2.4% solution?
2) One route to my weekend retreat is 180 miles with a speed limit of 60 mph. Another route is 150 miles, but I can only average 45 mph. If there is a construction delay on the faster route, how long a delay can I tolerate and still get to that destination in the same time it would take by the slower route?
