BIOL 1406

PreLab 1.2

**When measuring a random variable, what units of measurement should I use?**

Measurements of a random variable almost always consists of BOTH a number AND a
unit. Failure to use appropriate units along with the numerical value makes your
measurement incorrect. Scientists use the International System of Units (SI
units). SI is the modern version of the “metric system”. This system is
convenient for several reasons. For one, it is the standard used around the
world, which makes it easy for scientists to compare their results with each
other. For another, because SI units are related to each other by factors of 10,
it is easy to convert from one unit to another by simply moving the decimal
point to the left (if the units get bigger) or to the right (if the units get
smaller.)

Below is a review of several important SI units and their prefixes.

**International System of Units**

Random Variable | Unit | Abbreviation |

Distance | meter | m |

Weight | gram | g |

Volume | liter | L |

Time | second | s |

Amount of a substance | mole | mol |

**SI prefixes for units of measurement**

Prefix | abbreviation | relationship to basic SI unit | means multiply by: (to convert to basic SI unit) |

Micro | μ | one-millionth | 10^{-6} or 0.000001 |

Milli | m | one-thousandth | 10^{-3} or 0.001 |

Centi | c | one-hundredth | 10^{-2} or 0.01 |

Deci | d | one-tenth | 10^{-1} or 0.1 |

Deca | da | ten times | 10 |

Kilo | k | one thousand times | 1000 |

Mega | M | one million times | 1,000,000 |

Your Turn |
||

What are the SI units for measuring distance? | Check your answer. | |

What are the SI units for measuring weight? | Check your answer. | |

What are the SI units for measuring volume? | Check your answer. | |

How many millimeters are in 1 cm? | Hint | Check your answer. |

How many centimeters are in 1 km? | Hint | Check your answer. |

How many microliters are in 1 mL? | Hint | Check your answer. |

How many microliters are in 1 dL? | Hint | Check your answer. |

1 kg = ? mg | Hint | Check your answer. |

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