EASA / CAR Part-66 · Module 1 · 1.1 Arithmetic · Cat A
Objective: three ways of writing the same quantity. Slide the bar and watch the fraction, the decimal and the percentage move together, so you can see that converting between them changes the notation and nothing else.
A fraction is a division waiting to happen. Three eighths literally means 3 divided by 8, and doing that division gives the decimal 0.375. There is no separate conversion rule to learn, the fraction bar is the divide sign.
Per cent means per hundred. Multiplying the decimal by 100 restates it as a number of hundredths, so 0.375 becomes 37.5%. Going the other way, divide by 100. This is the conversion most often needed in tolerance and efficiency questions.
Simplifying does not change the value. Dividing top and bottom by the same number leaves the proportion untouched, which is why 4/8, 2/4 and 1/2 all sit at exactly the same place on the bar. Always give a final answer in its simplest form.