Word problems involving rates can be solved in a number of different ways. Observe how students solve these problems and encourage different methods for different situations. When proportions are set up involving rates, the units of measure should be included. The concept of slope is developed in Grade 10. In Grade 9, you can introduce the concept in a concrete manner as a ratio.
Students can also graph the relationship as a linear function.
Ratios can be compared by converting them to fractions, decimals, or percents and then comparing the results. Changing the context and numbers involved in problems changes the level of difficulty of the problem. Students have studied scale ratio and reading and interpreting scale drawings in previous grades. They have made scale drawings given a shape and a scale. These concepts should be reviewed before actually making scale drawings of objects.