Year 6 Mental Arithmetic: Sets 17 and 18
This week's sets of mental arithmetic questions for Year 6 are all about measurement. These questions highlight some key concepts, including the difference between finding the perimeter and the area of rectangles.
The perimeter is the total distance around the rectangle. Because a rectangle has two pairs of parallel sides there are several ways of working out the perimeter. Let's look at a rectangle which is 6 cm long and 5 cm wide.
Method 1. Add up all four sides: 6 cm + 5 cm + 6 cm + 5 cm = 22 cm
Method 2: Add 6 cm and 5 cm and then double the answer. 6 cm + 5 cm = 11 cm. 11 cm doubled = 22cm
method 3: Multiply 6 cm by 2 and 5 cm by 2 and add the totals.
6 cm x 2 = 12 cm. 5 cm x 2 = 10 cm. 12 cm + 10cm = 22 cm.
Remember, perimeter is measured in cm, but area is measured in sq. cm. as it is the amount of surface the rectangle covers. Area is calculated by multiplying the length by the width.
(6 cm x 5 cm = 30 sq cm.)
The other important fact children need to know for this set of questions is that the total of the three angles of a triangle always adds up to 180 degrees.