The unitary method is a technique in elementary algebra for solving a class of problems in variation. It consists of altering one of the variables to a single unit, i.e. 1, and then performing the operation necessary to alter it to the desired value.
For example, to solve the problem. 'A man walks seven miles in two hours. What is his average speed?', we aim to calculate how far the man walks in one hour. We can safely assume that he would walk half the distance in half the time. In one hour (one half of two hours) he walks three and a half miles (one half of seven miles). His speed is therefore three and a half miles per hour.
Naismith's rule is a rule of thumb that helps in the planning of a walking or hiking expedition by calculating how long it will take to walk the route, including ascents. This rule applies only to hikes rated Class 1 on the Yosemite Decimal System, and not to Class 2 or higher. The rule was devised by William W. Naismith, a Scottish mountaineer, in 1892. The basic rule is as follows:
The basic rule assumes hikers of reasonable fitness, on typical terrain, under normal conditions. It does not account for delays, such as extended breaks for rest or sightseeing, or for navigational obstacles. For planning expeditions a team leader may use Naismith's rule in putting together a route card.
The system of imperial units or the imperial system (also known as British Imperial) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The system came into official use across the British Empire. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, but some Imperial units are still used in the United Kingdom and Canada.
Many different units of length have been used around the world. The main units in modern use are U.S. customary units in the United States and the Metric system elsewhere. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.
The base unit in the International System of Units (SI) is the metre, defined as "the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second." It is approximately equal to 1.0936 yards. Other units are derived from the metre by adding prefixes from the table below: