Length and Perimeter — Tasmanian Year 4 Maths
Millimetres, converting between metres and centimetres, perimeter, and length word problems in everyday settings. Four subtopics and 80 questions with answers, aligned to AC9M4M01 and AC9M4M02.
Length and Perimeter in Tasmanian Year 4
This topic is about measuring and working with length. Students read rulers to the nearest millimetre, change between millimetres, centimetres and metres, work out the distance around shapes, and use all of this to solve everyday problems about how long, how far and how much longer.
The four subtopics below cover measuring length in millimetres, converting between metres and centimetres, calculating perimeter and solving length problems. Length and Perimeter is one of the 20 topics in Tasmanian Year 4 Maths and sits in the Measurement strand. It covers Australian Curriculum codes AC9M4M01 and AC9M4M02. These skills lead straight into Year 4 Area, where the space inside a shape is measured, and on to other metric units in later years.
Subtopics
Length and Perimeter: common questions
How do you change centimetres into millimetres?
Multiply by 10, because every centimetre is split into 10 millimetres: \(12\text{ cm} = 120\text{ mm}\). To go back, divide by 10, or split the length into whole centimetres and leftover millimetres, so 45 mm is 4 cm 5 mm. A common slip when measuring is to start from the 1 on the ruler instead of the 0.
How do you change metres into centimetres?
Multiply by 100, because \(1\text{ m} = 100\text{ cm}\), so \(9\text{ m} = 900\text{ cm}\). For a mixed length, change the metres and add the centimetres: 4 m 8 cm is \(400 + 8 = 408\) cm. Watch for 48 cm as an answer here, a common mistake that joins the digits instead of adding the lengths.
How do you find the perimeter of a rectangle?
Add all four sides. Opposite sides of a rectangle are equal, so a quick way is to add the length and the width, then double the total. A rectangle 11 m long and 6 m wide gives \(11 + 6 = 17\), and \(17 + 17 = 34\) m. The most common mistake is adding only one length and one width.
How can my child practise length at home?
Measure things around the house with a ruler and a tape measure, estimating first and checking after: small items like a key suit millimetres, and a hallway suits metres. Make up cutting problems too. If 65 cm is cut from a 2 m ribbon, change 2 m to 200 cm, then \(200 - 65 = 135\) cm is left.
Which curriculum codes cover Length and Perimeter in Tasmanian Year 4?
The topic comes under Australian Curriculum codes AC9M4M01, which is about reading scaled instruments and choosing suitable units when measuring and comparing, and AC9M4M02, which is about ways of measuring perimeter and area. Measuring in millimetres and converting between metres and centimetres sit under AC9M4M01; perimeter sits under AC9M4M02.