Kolmiosäännön

Kolmiosääntö, often translated as the "rule of three," is a mnemonic device used to estimate calculations involving proportions. It is particularly useful in situations where one needs to find a fourth value when three values are known, and the relationship between them is directly proportional.

The core principle of the rule of three is to set up a proportion. If we know that 'a' corresponds to 'b', and we want to find out what 'd' corresponds to when 'c' is the known value, the relationship is expressed as a/b = c/d. To solve for 'd', the formula derived from this proportion is d = (c * b) / a.

This method is commonly encountered in everyday scenarios, such as scaling recipes, calculating distances based on maps, or determining costs based on quantity. For example, if 5 apples cost $2, and you want to know the cost of 12 apples, you would set up the proportion: 5 apples / $2 = 12 apples / x dollars. Applying the rule of three, x = (12 * $2) / 5, which results in $4.80.

While effective for simple proportional problems, it's important to ensure the relationship between the quantities is indeed directly proportional. If the relationship is inverse, a different approach is required. The rule of three provides a straightforward and memorable way to tackle many common calculation needs.