In this video lesson, students use the context of shopping to explore how equivalent ratios and ratios involving 1 can be used to find unknown amounts. Students are introduced to the idea of unit price. They use the word “per” to refer to the cost of one item, and the phrase “at this rate” to indicate that the ratios of price to quantity are equivalent. They find unit prices in different situations and notice that they are useful in computing prices for other amounts (MP7). They use precision, verbally and in diagrams, (MP6) as they determine units for numbers in a ratio. 

They also apply these ideas to constant speed and through concrete experiences. Students measure the time it takes to travel a distance and use it to calculate and compare the speed they traveled in meters per second. Students learn that speed can also be described using the terms per and at this rate. The idea of a constant speed relating the quantities of distance and time is important in the development of students’ ability to reason abstractly about quantities (MP2).

Grade 6, Episode 3: Unit 2, Lessons 8 & 9 | Illustrative Math