Maths KS3

We have been concentrating on maths for the past few days.  We have been through:

Decimals
Adding, subtraction - the general rule is to proceed as normal or remove decimals and then reinsert the decimals at the end.
Multiplying - remove decimals, work out and then combine the number of decimals points in the answer.
Division - make a whole number by multiplying by 10 or 100 and then do long division.  The answer will be the same as if you had not multiplied by 10 or 100.
make it a whole number

Factors
Factors of  10 are 2 x 5.  Factors of 20 are 2 x 10 + 2 x 2 x 5  = 2squared x 5.

Prime numbers
Prime numbers only have 2 factors - 1 and themselves.
2,3,5,7,11,13,17 etc. 2 s the only even prime number.  To work out if it is a prime number:  is it divisable by 2,3,5,7?    If not then its a prime number.

HCF
Take the lowest factors (all of them) and work out.
LCM
Take the higests common factors (all of them) and work out

Math Revision

Multiples, factors, prime numbers...

Multiples

This is the times tables. Multiples of 5 are 10,15,20,25. Multiples of 7 are 14,28,35,42.

Factors

The factors of a number are all the numbers that go into that number EXACTLY. The factors of 30 are 1,2,3,5,6,10,15 and 30.

Prime Numbers

A prime number can only be divided by 1 and itself. Prime numbers less than 20 are 2,3,5,7,11,13,17 and 19.

A quick trick to work out prime numbers between 21 and 50 is to write out all the number and then cross out all even numbers. Also cross out mulitples of 3,5 and 7. The numbers that are left are all prime numbers.

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DID YOU KNOW:

1 is not a prime number. It only has 1 factor.

2 is the only even prime number.

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