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This True or False? routine prompts students to recall what they know about addition of fractions with a common denominator and about fractions that are equivalent to whole numbers. The understandings elicited here will be helpful later in the lesson when students find sums or differences of two fractions, or of a whole number and a fraction, to solve problems about the perimeters of rectangles with fractional side lengths.
Decide if each statement is true or false. Be prepared to explain your reasoning.
In this activity, students use their knowledge of feet and inches and the perimeter of a rectangle to solve problems in context. Given the perimeter and one length of a room, they determine its width, in feet, and the distance along two walls, in inches. Students could reason about each problem in a number of ways. As they interpret the quantities in the situation and represent them with expressions or equations, students practice reasoning quantitatively and abstractly (MP2).
A rectangular room has a perimeter of 39 feet and a length of feet.
Unknown Measurements Large Cards (groups of 12)
Unknown Measurements Small Cards (groups of 4)
This activity allows students to consolidate their learning from the past few units to solve problems about length measurements in a mathematical context.
First, students find the perimeter or unknown side length of various quadrilaterals. To do so, they apply what they know about adding and subtracting fractions and about rewriting certain fractions as whole numbers. Next, they determine which pairs of figures have a certain multiplicative relationship—for instance, which figure has a perimeter that is 9 times that of another figure. Because the measurements are in different units, students need to attend to the relationship between the units and perform conversions accordingly.
The activity can be done in the format of a Gallery Walk or by giving each group a full set of the diagrams from the blackline master.
Your teacher has posted six quadrilaterals around the room. Each one has an unknown side length or an unknown perimeter.
Choose two diagrams—one with an unknown side length and another with an unknown perimeter. Make sure all six shapes will be visited by at least one person in your group
Find the unknown values. Show your reasoning and remember to include the units.
Discuss your responses with your group until everyone agrees on the unknown measurements for all six figures.
Answer one of the following questions. Explain or show your reasoning.
Select students to briefly share the 6 unknown measurements and their reasoning. Display their calculations or record them for all to see. Then discuss how students reasoned about whether the comparison statements in the last problem were true.
“How did you know that the perimeter of B is 2 times that of D?” (I know that feet and inches are related, and that 1 foot is 12 inches. So I recognized that 24 inches is twice 1 foot.)
“How did you find a figure with a perimeter 1,000 times that of another figure?” (I know that a kilometer is 1,000 meters, so I started with A and E, converted their perimeters, and then checked if one perimeter is indeed 1,000 times as long as the other.)
“How did you know that the perimeter of F is 9 times that of B?” (I converted the yards into feet, and then I could see that 18 feet and 2 feet are related: .)
We solved problems and puzzles by converting units of measurement—gallons, quarts, cups, pounds, ounces, yards, feet, and inches—and by comparing measurements in different units. We saw that the problems could be solved in different ways.
For example, if Priya threw a disc 16 yards and this is 4 times as far as the distance Jada threw in feet, how far did Jada throw the disc?
One way to solve this problem is by finding , which is Jada’s throw distance in yards (), and then by multiplying the result to convert the yards to feet (, so 4 yards is 12 feet).
Another way is first to convert the 16 yards to feet (, so 16 yards is 48 feet), and then to divide the result by 4 to find Jada’s throw distance ().
In the last two lessons, we solved multiplication and comparison problems that involve the perimeter of rectangles and some other quadrilaterals.