maths smart grade 4 © 2012 alston publishing house pte ltd add mentally

Maths Sm

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2012 Alston Publishing House Pte LtdAdd mentally

Add mentallyM

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When we add numbers mentally, we are trying to find a quick way of adding the numbers in our heads.

Example:

Add 1473 and 206 mentally.

Maths Sm

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2012 Alston Publishing House Pte LtdArea

Area is a measure of the amount of space inside a flat shape or figure.

AreaM

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Maths Sm

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2012 Alston Publishing House Pte LtdCarroll diagram

Carroll diagramM

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A Carroll diagram helps us sort data in a ‘yes’ or ‘no’ manner. A simple Carroll diagram has two groups.

If the first group is labelled ‘A’, then the second group is usually labelled ‘Not A’.

We can further sort the data in the two groups into two more groups to get four groups as shown.

Carroll diagramM

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Example:

or

This Carroll diagram sorts the animals according to whether they are owls and whether they are brown.

Maths Sm

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2012 Alston Publishing House Pte LtdCount back

Count backM

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Counting down from a bigger number to a smaller number.

Example: To get from 6231 to 4000, we count back in thousands first, then hundreds, tens and finally ones.

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2012 Alston Publishing House Pte LtdCount on

Count onM

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Counting up from a smaller number to a bigger number.

Example: To get from 3787 to 6000, we count on in thousands first, then hundreds, tens and finally ones.

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2012 Alston Publishing House Pte LtdDecimal

DecimalM

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A fraction can be written as a decimal. A decimal has a whole number part and a fraction part that is separated by a decimal point.

Example:

65.27 is a decimal number.

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2012 Alston Publishing House Pte LtdDecimal point

Decimal pointM

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A decimal point separates the whole number part from the fraction part of the number.

Example:

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DoubleM

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When we find the double of a number, we add the number to itself.

Example:

Double 2550.

So, double 2550 is 5100.

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DurationM

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The amount of time an event lasts for (between starting time and ending time).

Example:

A cooking class started at 3.30 p.m. and ended at 5.30 p.m. What was the duration of the cooking class?

The duration of the cooking class was 2 h.

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HalfM

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When we find half of a number, we divide the number by 2.

Example:

Half of 6700.

So, half of 6700 is 3350.

Maths Sm

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2012 Alston Publishing House Pte LtdHundredth

HundredthM

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When we divide one whole into 100 equal parts, each part is one hundredth of the whole.

Example:

(1 hundredth) = 0.011001

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2012 Alston Publishing House Pte Ltd

Improper fraction

Improper fractionM

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An improper fraction has a numerator that is greater than or equal to its denominator. The value of an improper fraction is equal to or greater than 1.

Example:

The improper fraction represented by the shaded partsis .34

Maths Sm

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2012 Alston Publishing House Pte LtdMillimetre (mm)

Millimetre (mm)M

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A unit of measurement for length.

Example:

The length of the nail is 18 millimetres (or 18 mm).

Maths Sm

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2012 Alston Publishing House Pte LtdMixed number

Mixed numberM

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A mixed number is made up of a whole number and a fraction. The value of a mixed number is always greater than 1.

Example:

The mixed number represented by the shaded parts is .

431

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Multiply mentally

Multiply mentallyM

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When we multiply numbers mentally, we are trying to find a quick way of multiplying the numbers in our heads.

Example:

Multiply 6 and 30 mentally.

Maths Sm

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2012 Alston Publishing House Pte LtdPerimeter

PerimeterM

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The perimeter of a figure is the total distance around all the sides of the figure.

Example:

The perimeter of the rectangle is 14 cm.

Maths Sm

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2012 Alston Publishing House Pte LtdProper fraction

Proper fractionM

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A proper fraction has a numerator that is smaller than its denominator. The value of a proper fraction is between 0 and 1.

Example:

The proper fraction represented by the shaded part is .31

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Round to the nearest tenth

Round to the nearest tenthM

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When we round a number to the nearest tenth, we look at the digit in the hundredths place.(a)If the digit < 5, we round it to the smaller tenth.(b)If the digit > 5, we round it to the bigger tenth.(c)If the digit = 5, we round it to the bigger tenth.

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Round to 1 decimal place

Round to 1 decimal placeM

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Rounding to 1 decimal place is the same as rounding to the nearest tenth.

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2012 Alston Publishing House Pte Ltd

Round to the nearest whole

number

Round to the nearest whole numberM

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When we round a number to the nearest whole number, we look at the digit in the tenths place.(a)If the digit < 5, we round it to the smaller wholenumber.(b)If the digit > 5, we round it to the bigger whole number.(c)If the digit = 5, we round it to the bigger whole number.

Maths Sm

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2012 Alston Publishing House Pte Ltd

Square centimetre (cm2)

Square centimetre (cm2)M

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A unit of measurement for area.

Example:

The area of the square is 1 square centimetre (or 1 cm2).

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Square metre (m2)

Square metre (m2)M

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A unit of measurement for area.

Example:

The area of the square is 1 square metre (or 1 m2).

Maths Sm

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2012 Alston Publishing House Pte LtdSquare unit

Square unitM

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A unit of measurement for area.

Example:

The area of the figure is 6 square units.

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Subtract mentally

Subtract mentallyM

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When we subtract numbers mentally, we are trying to find a quick way of subtracting the numbers in our heads.

Example:

Subtract 302 from 8348 mentally.

Maths Sm

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2012 Alston Publishing House Pte LtdTenth

TenthM

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When we divide one whole into 10 equal parts, each part is one tenth of the whole.

Example:

(1 tenth) = 0.1101

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2012 Alston Publishing House Pte LtdTime line

Time lineM

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We use a time line to help us calculate duration.

Example:

Ari’s birthday party began at 11.30 a.m. and ended at 2.50 p.m. The duration of the party was 3 h 20 min.

Maths Sm

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2012 Alston Publishing House Pte LtdVenn diagram

Venn diagramM

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A Venn diagram uses circles to help us sort data into different groups.

Example:

This Venn diagram sorts the data according to whether they are multiples of 2, multiples of 5 and/or two-digit numbers.