Primary 3 Mathematics revision reference

Use this page to recall a method, then return to the lessons for pictures, explanations and practice.

Whole numbers and remainders

Read place value from thousands to hundreds, tens and ones. In a written calculation, align the places before you start.

For division by a positive whole number:

dividend = divisor × quotient + remainder.

The remainder is at least zero and smaller than the divisor. For example, 23÷5 = 4 remainder 3, because 5 × 4 + 3 = 23.

Use the context to decide what to do with a remainder: 23 children need 5 cars if each car holds 5 children.

Equivalent fractions

Multiplying or dividing the numerator and denominator by the same nonzero whole number keeps the value unchanged. For example, 2/3 = 4/6.

To compare unlike fractions, express them in the same fractional unit. To add or subtract related fractions, change to a common denominator first:

1/2 + 1/4 = 2/4 + 1/4 = 3/4.

For the fraction comparisons and sums in this course, given denominators stay at most 12 and sums stay within one whole.

Measurement units

1 km = 1000 m; 1 m = 100 cm.
1 kg = 1000 g; 1 ℓ = 1000 ml.

Larger unit to smaller unit: multiply by the number of smaller units in one larger unit. Reverse the conversion by dividing.

For example, 2 m 35 cm = 235 cm. Keep the unit beside the answer.

For time, 1 hour is 60 minutes and 1 minute is 60 seconds. Count through the hour boundary if needed: from 09:45 to 10:15 is 15 minutes to 10:00 and 15 more minutes, or 30 minutes. In 24-hour time, 15:20 means 3:20 pm.

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.

Perpendicular lines meet at a right angle. Parallel lines stay the same distance apart and do not meet. A right angle is a square corner.

Reading a bar graph

Read the title, axis labels, units and scale. Equal spaces on the value axis represent equal increases. A bar reaching 4 intervals on a scale of 5 represents 20, not 4.