Ratios and Proportions
A ratio expresses the relationship between two quantities. The ratio of 3 to 4 can be written as 3:4 or 3/4.
A proportion states that two ratios are equal: a/b = c/d. To solve for an unknown, cross-multiply: a × d = b × c.
Rate is a ratio comparing two different units (miles per hour, dollars per pound). A unit rate reduces the denominator to 1 (e.g., $2.50 per pound).
Example: If 5 lb of apples cost $8.75, how much do 8 lb cost? Set up: 5/8.75 = 8/x → 5x = 70 → x = $14.00