978-1-4730-0924-0 (.epub)

Add 5: | 3 + 5 = 8 |

Double it: | 8 × 2 = 16 |

Subtract 8: | 16 – 8 = 8 |

Divide by 2: | 8 ÷ 2 = 4 |

Take away number: | 4 − 3 = 1 |

Add 4: | 1 + 4 = 5 |

Instruction | Expression |
---|---|

Think of a number | n |

Add 5 | n + 5 |

Double it | n + 5 + n + 5 = 2 × n + 10 |

Subtract 8 | 2 × n + 10 – 8 = 2 × n + 2 |

Divide by 2 | (2 × n ÷ 2) + (2 ÷ 2) = n + 1 |

Take away the number you first thought of | n + 1 − n = 1 |

Add 4 | 1 + 4 = 5 |

Instruction | Expression |
---|---|

Think of a number between 1 and 10 | n |

Multiply by 4 | 4 × n |

Add 6 | 4 × n + 6 |

Divide by 2 | (4 × n ÷ 2) + (6 ÷ 2) = 2 × n + 3 |

Subtract 3 | 2 × n + 3 – 3 = 2 × n |

Divide by 2 | 2 × n ÷ 2 = n |

add 4: | 17 + 4 = 21 |

divide by 3: | 21 ÷ 3 = 7 |

subtract 5: | 7 − 5 = 2 |

All positive even integers bigger than or equal to 4 can be expressed as the sum of two primes.

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