Imagine a situation when a man wants to buy a red coloured shirt, so he goes to a store. The shopkeeper speaks only English. The man says, “Ureed qameesan ahmar allawn”. The shopkeeper says, “What?!” The man asked for a red colored shirt, but he said it in Arabic. Obviously, the shopkeeper couldn’t understand anything since it was not a standard language.

Similarly, there are many systems and units in place for measuring different quantities like length, area, mass, volume and other things. For example, an acre is a common way of representing area measurement in India. One acre is around 4046 square meters if you look at the metric system. So now you can guess how difficult it would be if there were no standard units and measurement.

Similarly temperature is measured in degree Celsius and the same unit of measurement cannot be used to measure the length of a rod. Each quantity has to be measured in its own way. Magnitude and the measurement varies along with the quantity. Hence the need for the units of measurement for each quantity arises.

The International System of Units or SI units defines standard units for measurement of all physical quantities. In principle, any physical quantity can be expressed in terms of seven base units.

The Seven Base Unit | ||

Property | Unit | Symbol |

Length | Meter | m |

Mass | Kilogram | kg |

Time | Second | s |

Electric Current | Ampere | A |

Temperature | Kelvin | K |

Amount of Substance | Mole | mol |

Luminous Intensity | Candela | cd |

Apart from the base units, there are SI units of derived units. These are called as such because their value is determined based on one or more base units. Some examples are given below:

- Frequency – Hertz (Hz); 1 Hz = 1 s
^{-1}

- Power – Watt (W); 1 W = 1 kg·m
^{2}s^{−3}

The SI system utilizes a standard system of prefixes to the basic units that allow them to be more relevant to and descriptive of relative magnitude.

Prefixes are used to identify the multiples or the fractions of the original unit. There are 20 accepted prefixes.

The table below lists the standard prefixes for the SI units of measurement.

Roman numerals 1 to 100 can be obtained by using any of the two given below methods:

**Method 1:**In this method, we break 65 into the least expandable form, write their respective roman letter and add/subtract them, i.e. 65 = 50 + 10 + 5 = L + X + V = LXV

**Method 2:**In this method, we consider the groups of numbers for addition such as: 65 = 60 + 5 = LX + V = LXV

Certain rules are to be followed while writing roman numbers from 1 to 100. These rules are explained here in detail.

- When a bigger letter precedes a smaller letter, the letters are added. For example: CX, C > X, so CX = C + X = 100 + 10 = 110.

- When a smaller letter precedes a bigger letter, the letters are subtracted. For example: IV, I < V, so IV = V – I = 5 – 1 = 4.

- When a letter is repeated multiple times, they get added. For example: MMM = M + M + M = 1000 + 1000 + 1000 = 3000

- The same letter cannot be used more than three times in succession. V, L, and D cannot be repeated, they appear only once.

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