Area, Perimeter & Shapes: 3rd grade math in Lapland

Area in square units and by multiplying, perimeter, right angles, parallel lines and shapes.

Follow the reindeer across snowy fells in Sápmi, under the dancing northern lights. Characters here greet you with “Buorre beaivi!” (good day in North Sámi), and eggs hatch into hybrids of animals like reindeer, moose, Arctic fox and red fox.

What your child practices

Follows Measurement & Data — Area and Perimeter (3.MD.C–D) and Geometry (3.G).

• Area in square units

  Find area by counting squares, and choose square centimeters or square meters.

  3.MD.C.5, 3.MD.C.6

• Area by multiplying

  Find the area of rectangles and squares by multiplying length by width.

  3.MD.C.7

• Perimeter

  Add the sides all the way around rectangles, squares and other shapes.

  3.MD.D.8

• Area and perimeter of L-shapes

  Split L-shapes into rectangles to find their area, and add every side for the perimeter.

  3.MD.C.7d, 3.MD.D.8

• Area and perimeter word problems

  Solve fence, floor and garden problems with area and perimeter.

  3.MD.C.7b, 3.MD.D.8

• Right angles and turns

  See angles as turns, find right angles, and compare angles with a right angle.

  4.MD.C.5

• Parallel and perpendicular lines

  Spot lines that never meet and lines that meet at a square corner.

  4.G.A.1

• Quadrilaterals

  Sort 4-sided shapes: squares, rectangles, rhombuses and other quadrilaterals.

  3.G.A.1

Try a problem from Lapland

Every problem is a short story set in the world. These are real problems from the game. Kids get endless new ones with different numbers.

Common mistakes, and how to help

Every wrong answer in Mixmonde is planned: it points to a named mistake, and the tip after a miss explains it with that problem’s numbers. These are the mistakes this world watches for, grouped the way the grown-ups’ dashboard shows them.

• Units and measuring

  The number is fine but the unit is off: a missing conversion (cm and m), the ruler not started at zero, or area mixed up with perimeter.

  Mistakes we catch: counted one row, added rows and columns, counted the edge, picked a square unit of the wrong size, used a length unit for area, mixed up area and perimeter, added the sides, added only two sides, missed a side, counted the missing corner, added the corner instead of taking it away, used only one part, fenced a side that is a wall and shared over 2 sides, not 4.

  Try at home: Measure the same table in cm and in m. Walk around a rug for perimeter, then cover it with sheets of paper for area.

• Choosing the operation

  The arithmetic is fine, but the wrong operation was picked: adding when the story takes away, or multiplying when it shares out.

  Mistakes we catch: subtracted instead of dividing and multiplied instead of dividing.

  Try at home: Read a word problem together and draw it as a quick picture or bar before choosing + − × ÷. Ask “is the answer bigger or smaller than the numbers we started with?”

• Shapes and angles

  Shape properties: counting sides, corners or faces, symmetry, naming angles, measuring with a protractor or radius vs diameter.

  Mistakes we catch: mixed up smaller and greater, called it a right angle, missed the right angle, counted every corner, judged the angle by its arms, mixed up parallel and perpendicular, missed parallel lines, missed the square corner, called every crossing perpendicular, called crossing lines parallel, counted sides, not pairs, missed a pair, missed that it has 4 sides, miscounted the sides, ignored the side lengths, ignored the corners and thought a square is not a rectangle.

  Try at home: Fold paper shapes to find lines of symmetry. Use the corner of a sheet of paper as a right-angle checker around the house.

More Grade 3 worlds: Numbers to 10,000 · Multiplication & Division · Fractions · Measuring & Graphs · Time & Money