## Substitution

Assigning values to a pronumeral is called substitution.

#### Example 2

Algebraic expression | Solution | |
---|---|---|

5\(x\) | 5 × 4 | = 20 |

\(x\) + 3 | 4 + 3 | = 7 |

\(x\) – 1 | 4 – 1 | = 3 |

\(\dfrac{x}{2}\) | \(\dfrac{4}{2}\) | = 2 |

#### Example 3

Algebraic expression | Solution | |
---|---|---|

\(a + b\) | 6 + 5 | = 11 |

\(a\ – b\) | 6 – 5 | = 1 |

10 – \(a\) | 10 – 6 | = 4 |

\(4a\ – 3b\) | 4 × 6 – 3 × 5 | = 24 – 15 = 9 |

#### Example 4

Algebraic expression | Solution | |
---|---|---|

x^{2} + 1 |
3^{2} + 1 |
= 9 + 1 = 10 |

x^{2} – 4 |
362 – 4 | = 9 – 4 = 5 |

4x^{2} + 2 |
4 × 3^{2} + 2 |
= 4 × 9 + 2 = 36 + 2 = 38 |

2x^{2} – 4 |
2 × 3^{2} – 4 |
= 2 × 9 – 4 = 18 – 4 = 14 |

#### Example 5

The cost of hiring an electric saw for n hours is (3n + 20) dollars. How much does it cost to hire the saw for 3 hours?