Scientific Understanding

**What sections should I know before attempting to learn this section?**

—> Introduction to Significant Figures

**How do you add or subtract significant figures?**

Whenever you add or subtract significant figures you have to make sure your answer to that mathematical step reflects the figures that it came from. In terms of addition and subtraction, this focuses around what the decimal places is of the numbers you are adding or subtracting. The number with the least amount of accuracy provides us with a limited amount of decimal places. Let us demonstrate below.

**Examples**: Give the answer to the addition and subtraction problems with the correct number of significant figures.

78.2 + 63.14 = ?

Calculator Shows | Correct Answer |

141.34 | 141.3 |

3.2 – 76.8914 = ?

Calculator Shows | Correct Answer |

–73.6914 | –73.7 |

900 + 320 – 2000 + 60 = ?

Calculator Shows | Correct Answer |

–720 | –1000 |

**VIDEO Adding and Subtracting Significant Figures Demonstrated Example 1**: What would the answer be to the correct number of significant figures for the problem below?

**8.635 + 12 = ?**

What answer do I get on calculator when I add them?

Answer : 20.635

Which figure has the least amount of decimal places?

Answer: 12

To what decimal place does 12 have?

Answer: the ones place

What decimal place should my answer stop at?

Answer: the ones place

How do I round 20.635 to the ones place?

COMPLETE ANSWER: 21

**VIDEO Adding and Subtracting Significant Figures Demonstrated Example 2**: What would the answer be to the correct number of significant figures for the problem below?

**23 + 700 – 48.1 + 89 = ?**

What answer do I get on calculator when I add and subtract them?

Answer : 763.9

Which figure has the least amount of decimal places?

Answer: 700

To what decimal place does 700 have?

Answer: the hundreds place

What decimal place should my answer stop at?

Answer: the hundreds place

How do I round 763.9 to the hundreds place?

COMPLETE ANSWER: 800

**PRACTICE PROBLEMS**: Determine the answer with the correct significant figures for the problems below.

800 + 90 = | 900 |

61.48 – 85 = | –24 |

0.76 + 1.3659 = | 2.13 |

0.00528 + 0.0063 = | 0.0116 |

6.3 + 40 – 14 + 21.75 = | 50 |

96.32 – 17.4 – 237.15 = | –158.2 |