2.2 Halve  (Page 4/4)

I used a circle in my design. I am saying no more.

• How can we draw a circle?

Use any round object to draw it, or a stencil, or a pair of compasses. At home you can use a plate if you want to draw a circle.

• What do we know about circles?

They are round and have no angles. Look at the circle below and then we’ll learn more about circles:

AB is the diameter. It halves the circle.

• All lines that you draw from the centre to the circumference of the circle will be exactly the same length. We call such a line the radius of the circle.
• Take a piece of string or wool and lay it precisely on the circular line (the circumference). Measure the length of the string on your ruler. That is how you can measure the circumference of a circle.

• Bonny and Tommy are very keen to work with circles.

• Measure the radius and the circumference of each circle and write it down here.

Circle P: Radius = _____cm Diameter = _____cm

Circle Q: Radius = _____cm Diameter = _____cm

Circle R: Radius = _____cm Diameter = _____cm

• What have you discovered?________________________________________

Now we know: 2 x Radius = Diameter and Diameter ÷ 2 = Radius

• Use this to calculate the lengths:

Circle W: Radius = 5cm Diameter = _____cm (Double)

Circle X: Radius = 8cm Diameter = _____cm

Circle Y: Diameter = 12cm Radius = _____cm (Halve)

Circle Z: Diameter = 22cm Radius = _____cm

• How can you find the centre of a circle that has been drawn without a pair of compasses?

Draw 2 circles that are exactly the same size. Cut out one of the circles. Fold it exactly in half and then in half again. Open it out and find the spot where the 4 folds cross in the centre. That is the centre of the circle. Lay it exactly on the other circle and push a pin down through the centre to make a mark on the circle below. Try it at home and come and show it to the class.

• This circle is divided into 4 equal parts. It is divided into 4 quarters.

• Sometimes Bonny and Tommy share their sweets with Mommy and Daddy.
• Can you still remember how we folded the circle into 4 equal parts? We folded the circle in half and then in half again.
• That is exactly what they do with the sweets.

All multiples of 4 can easily be divided into quarters like this.

• Count in multiples of 4 up to the 10th multiple and back again.

• Complete the table.

• Thus: ÷ 4 is the same as halving 2 times.

Assessment

Learning Outcome 1: The learner will be able to recognise, describe and represent numbers and their relationships, and to count, estimate, calculate and check with competence and confidence in solving problems.

Assessment Standard 1.4: We know this when the learner orders, describes and compares numbers:

Assessment Standard 1.7: We know this when the learner solves and explains solutions to practical problems that involve equal sharing and grouping and that lead to solutions that also include unitary and nonunitary fractions (e.g. ¼, ¾);

Assessment Standard 1.8: We know this when the learner can perform calculations, using appropriate symbols, to solve problems;

Assessment Standard 1.10: We know this when the learner uses the following techniques:

1.10.1 building up and breaking down numbers;

1.10.2 doubling and halving;

1.10.3 number-lines;

1.10.4 rounding off in tens.

Learning Outcome 3: The learner will be able to describe and represent characteristics and relationships between two-dimensional shapes and three-dimensional objects in a variety of orientations and positions.

Assessment Standard 3.1: We know this when the learner recognises, identifies and names two-dimensional shapes and three-dimensional objects in the environment and in pictures;

Assessment Standard 3.3: We know this when the learner observes and creates given and described two-dimensional shapes and three-dimensional objects using concrete materials (e.g. building blocks, construction sets, cut-out two-dimensional shapes, clay, drinking straws);

Learning Outcome 4: The learner will be able to use appropriate measuring units, instruments and formulae in a variety of contexts.

Assessment Standard 4.6: We know this when the learner investigates (alone and/or as a member of a group or team) and approximates.