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Helpful Facts
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- Pairs that equal 10 are very important
- When brackets are used, work out the sum in brackets first.
- Use known facts to help work out other facts. Use the facts for the 2x, 5x, 10x tables to help you work out others. 5x8=40, so 6x8 is 8 more ... 48.
- Multiples are numbers in that x table.
- Multiples are numbers in that x table.
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- Factors are numbers which will divide exactly into other numbers.
- Prime Numbers can only be divided by themselves and 1 (1 is not a Prime Number).
- To make a square number multiply by itself .
- When looking for a pattern in a number sequence, look at the difference between consecutive numbers.
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Addition
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- addition can be done in any order.
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- Knowing doubles can help you (e.g. 50+50=100, 51+53=104).
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- addition and subtraction are opposites (e.g. 58+46=104, 104-46=58).
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- 9, 11, 99, 101, 19, 21 are all nearly numbers. Adding 9: add 10 and subtract 1.
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- Add the tens then the units when adding mentally (e.g. 47+36 ... 47+30=77, 77+6=83).
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- Breaking up numbers can help add up mentally 49+37 is (40+9)+(30+7). Add the tens then add the units, add the nearest decade then adjust.
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Subtraction
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- To find the difference between two numbers, subtract them.
- Subraction and addition are opposites.
- When subracting close numbers count on or back.
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- When subtracting mentally count on using the shopkeepers method. e.g. for 93-58 count on from 58 to 60 (hold 2 in your head), count on from 60 to 90 (hold 30 in your head) and count on from 90 to 93 in your head (then add the 2, 30 and 3 together).
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Multiplication
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- Multiplication and division are opposites.
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- Approximate the answer first.
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Division
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Whole numbers are divisible by:
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10 if the last digit is 0 (350, 2900, 6730)
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5 if the last digit is 5 or 0 (455, 260, 365).
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2 if the last digit is even (244, 876, 990).
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3 if the sum of the digits is divisible by 3.
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4 if the last 2 digits are divisible by 4.
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6 if it is even and also divisible by 3.
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8 if half of it is divisible by 4.
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9 if the sum of the digits is divisible by 9.
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Estimate the answer first !
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Decimals
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- The decimal point separates: whole numbers from parts of numbers, whole numbers and tenths.
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- tenths, hundredths can be written as decimals 3/10=0.3.
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- Common fractions and decimals and percentages:
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0.5 = 1/2 = 50%
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0.25 = 1/4 =25%
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0.10 = 1/10 = 10%
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0.75 = 3/4 = 75%
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0.2 = 1/5 = 20%
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Shape and Space
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- There are 90 degrees in a right angle.
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- There are 360 degrees in a full turn.
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- There are 180 degrees in a half turn.
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- Angles less than 90 degrees are called ‘acute’.
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- Angles that are greater than 90 degress but less than 180 degrees are called ‘obtuse’.
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- There are three types of triangle: equilateral, isosceles and scalene.
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