# We will be working with the metric system tomorrow and I need two examples of things that come in sets of ten.

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Fingers and toes come in sets of ten, and bowling pins and billiard balls come in sets of ten.

There are also things that come in multiples of ten. For example, money. U.S currency has a 10 dollar bill, a twenty dollar bill, a 50 dollar bill, a 100 dollar bill, and a 1000 dollar bill, all multiples of 10. Multiples and powers of ten are easy to deal with mathematically because we just have to move the decimal point to multiply or divide by 10. That's why the metric system is so convenient.

The metric system is based on powers of ten. It's easy to convert from one metric unit to another because the conversion factors are all powers of ten. For example, lets say you need to convert 2500 meters to kilometers. Kilo means 1000, telling us that one kilometer is 1000 meters. We can multiply 2500 m by the unit factor 1 km/1000 m, which means we're dividing 2500 by 1000 to get 2.5 km. Since 1000 is 10^3, we divided by three powers of ten so we just moved the decimal point three places. Most metric conversions are just mental math, unlike conversions in other systems of measurement.