Primary 4 Mathematics revision reference

Use these reminders beside the Primary 4 lessons. Check the unit, number of decimal places and requested form before giving an answer.

Rounding, factors and multiples

≈ means approximately equal. To round, find the two nearest multiples of the requested place and choose the nearer one; halfway rounds up for the positive numbers used here. Thus 3467 ≈ 3500 to the nearest hundred.

A factor divides a number exactly. A multiple is a whole-number multiple of a number. The common factors of 12 and 18 are 1, 2, 3 and 6.

Fractions and decimals

Convert a mixed number by counting all its fractional parts: 2 3/5 = 13/5. For addition and subtraction, first use a common denominator. The denominator describes the part size, so it is not added.

Tenths, hundredths, thousandths are the first three places after the decimal point. 0.4 = 0.40: a trailing zero does not change the value.

For addition and subtraction, align the decimal points.
For multiplication by a one-digit whole number, estimate first and keep track of the decimal places.
For division, share the place values and exchange when needed.
3/20 = 15/100 = 0.15.

Area and perimeter

Perimeter is the distance around the outside. Area measures the surface inside.

For a rectangle with length l and width w:

P = 2(l + w), A = lw.

For a square with side s:

P = 4s, A = s².

Use matching length units before multiplying. A rectangle 6 cm by 4 cm has perimeter 20 cm and area 24 cm².

For a composite figure, split the area into rectangles without overlaps or gaps. For its perimeter, count only the outside edges; an internal dividing line is not part of the perimeter.

To find a missing width, use w = A÷ l. If you know the perimeter, first find half of it: w = P÷2-l. Use the right relationship for the information given.

Angles, symmetry and solids

In ∠ABC, the middle letter B names the vertex. A degree, written °, measures an angle. Put a protractor’s centre on the vertex and read the scale that begins at zero on the starting arm.

A line of symmetry divides a figure into matching mirror images. Turning a figure does not change its properties. A square has 4 equal sides and 4 right angles; a rectangle has 4 right angles and opposite sides equal.

A net folds into a solid. Count faces and check which edges meet; a flat drawing of a solid is not itself a net.

Tables, line graphs and pie charts

Read the title, headings, scale and units before comparing values. A line graph shows how a quantity changes across its horizontal axis. A pie chart compares parts of one whole; a larger sector represents a larger share.