GoalPlay an area and perimeter game and practise mixed facts with +, −, × and ÷.
New words
perimeter · the distance around a shapearea · the number of square units inside a shapemixed facts · facts that use different operations
Explanation
Here is a game for two players. Roll two dice. The numbers are the length and width of a rectangle. Find its area (length × width) and its perimeter (add all four sides). The player with the bigger area gets a point. If the dice show 5 and 3, the area is 5 × 3 = 15 square cm and the perimeter is 5 + 3 + 5 + 3 = 16 cm. Different rectangles can have the same perimeter and different areas. In mixed practice, read the sign each time: + means add, − means take away, × means equal groups and ÷ means share. A year of mathematics has given us many facts. Check each answer with the opposite operation: + with −, and × with ÷.
Worked examples
Roll the dice. They show 4 and 6, so the rectangle is 6 cm by 4 cm. The area is 6 × 4 = 24 square cm and the perimeter is 6 + 4 + 6 + 4 = 20 cm.
Rectangle
Perimeter
Area
6 by 2
16 cm
12 square cm
5 by 3
16 cm
15 square cm
4 by 4
16 cm
16 square cm
These three rectangles have the same perimeter, 16 cm, but different areas. The more square the rectangle is, the greater its area.
Problem
Answer
Check
56 + 27
83
83 − 27 = 56
91 − 38
53
53 + 38 = 91
7 × 8
56
56 ÷ 8 = 7
72 ÷ 9
8
9 × 8 = 72
Mixed facts: use the sign to decide what to do, then check with the opposite operation.
Class activity
Dice rectangles. Play the game in the lesson with a partner. Roll two dice ten times and write the rectangle each time with its area and perimeter. Who won more rounds? Then write four mixed problems, one for each operation, and check each answer with the opposite operation.
Practice
1
Find the area and perimeter of the rectangle.
Area: 8 × 5 = 40 square cm. Perimeter: 8 + 5 + 8 + 5 = 26 cm.
2
The dice show the dots in the picture. They give the length and width of a rectangle in cm. Find the area and the perimeter.
The dice show 3 and 6. Area: 3 × 6 = 18 square cm. Perimeter: 3 + 6 + 3 + 6 = 18 cm.
