Solve proportions by finding the missing value in a:b = c:d relationships. Perfect for cross multiplication, recipe scaling, unit conversion, and real-world ratio problems.
A proportion states that two ratios are equal. Written as a:b = c:d or a/b = c/d, it means the relationship between a and b is the same as between c and d. Cross multiplication (a×d = b×c) is the key to solving proportions.
This fundamental property allows us to solve for any unknown value by rearranging the equation. It works because multiplying both sides by b×d maintains equality.
Pro Tip: When setting up word problems, identify what stays constant (the ratio) and what changes. Write known values in the same positions: if comparing “part to whole”, keep parts in numerators and wholes in denominators consistently.