Page 8 - 新思维数学学生用书8 样章

1 Integers

Getting started

1 a Find all the prime numbers less than 20.
b Show that there are two prime numbers between 20 and 30.
2 a Find all the factors of 18.

b Find all the 2-digit multiples of 18.
c Find the highest common factor of 18 and 12.
d Find the lowest common multiple of 18 and 12.

3 Work out
a −+63 b −−63 c −×63
d −÷63 e 8+− 10 f −− − 9
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4 Write whether each of these numbers is a square number, a cube number or both.
a 49 b 27 c 1000

d 64 e 121 f 225
5 Find
a 100 b 3 125 c 15 − 12 2
2
Prime numbers have exactly two factors, 1 and the number itself.

Some examples of prime numbers are 7, 31, 83, 239 and 953.
The number 39 is the product of two prime numbers (3 and 13).

It is quite easy to find these two numbers.
The number 2573 is also the product of two prime numbers (31 and 83). It is much harder to find
the two numbers in this case.
It is easy to multiply two prime numbers together using a calculator or a computer.

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