Fractions - Addition and substraction
To add or subtract fractions we first rewrire each fraction so that they all have the same denominator(this is known as common denominator). The denominator is chosen to be the lowest common multiple of the original denominators. Then the numerators are added or substracted as apprpriate, and the result is divided by a common denominator.
Fractions - Multiplication
The product of two or more fractions is found by multiplying their numerators to form a new numerator, and then multiplying their denominators to form a new denominator.
Fractions - Division
To divide one fraction by another fraction, we invert the second fraction and then multiply. When we invert a fraction we interchange the numerator and denominator.