Grade 3 Math Unit11.2 Missing Side Lengths and Perimeter | How to Find the Unknown Side

Today's lesson is missing side lengths, found either off the side facing the blank or out of the fence when the perimeter is given. Opposite sides of a rectangle match, so a blank top over a four-unit bottom reads four units Sides of four and three make the whole ring: four plus three plus four plus three is fourteen units A twenty-unit fence with long sides of six leaves eight for the two ends, four units each A fourteen-unit fence whose ends are two units each leaves five units for every long side On a square one side of five units settles it: five four times gives the twenty-unit perimeter On a stepped floor the two broken top runs together reach the four-unit bottom Pupils finish able to supply a side that has no number from the side facing it or from a given perimeter, and to check by adding round. CHAPTERS 0:00 A number goes missing: today the shape tells you what to write 0:51 The promise a rectangle keeps: opposite sides match 2:06 Two sides tell you all four: reading a blank side 3:46 The harder route: the fence is given, the side is not 5:07 The square: one side is enough for the whole floor 6:15 When the long side is the one with no number 7:30 A stepped floor: the broken runs add up to the whole 8:51 Mixed practice: both ways to find a missing side 10:12 Two ways to find a missing side, and what to practise