Percentage = (Part ÷ Whole) × 100. Divide the part by the whole, then multiply by 100.

Percent = (A / B) × 100. 'A is what percent of B?' → divide A by B and multiply by 100.

Dividing by a fraction = multiplying by its reciprocal. a/b ÷ c/d = a/b × d/c.

Consecutive even integers differ by 2: n, n+2, n+4, ... Similarly, consecutive odd integers also differ by 2.

Celsius = (Fahrenheit - 32) × 5/9. Remember to subtract 32 first, then multiply by 5/9.

Speed = Distance / Time. Rearranged: Distance = Speed × Time; Time = Distance / Speed.

|x| = -x when x is negative. Absolute value always returns a non-negative result.

Find the Least Common Denominator (LCD), convert each fraction, then add the numerators.

Percentage decrease = (Old - New) / Old × 100. Divide the decrease by the original value.

Percentage increase = (New - Old) / Old × 100. Always divide by the original (Old) value.

Area of square = side². Perimeter = 4s. Don't mix the two formulas.

Terminating decimals end (0.75). Repeating decimals have a repeating block (0.333...). Both are rational numbers.

GCF is the Greatest Common Factor — the largest number that divides evenly into both numbers.

Diagonals = n(n-3)/2, where n is the number of sides. A square (n=4): 4(1)/2 = 2 diagonals.

Even + Even = Even. Also: Odd + Odd = Even. Even + Odd = Odd.

To convert fraction to decimal, divide the numerator by the denominator. Example: 3/4 = 3 ÷ 4 = 0.75.

Average speed = Total Distance / Total Time. Do NOT simply average the two speeds — that gives wrong answers.

a ≡ b (mod n) means a and b have the same remainder when divided by n. Example: 17 ≡ 2 (mod 5) since both give remainder 2.

Distance on a number line = |x₂ - x₁|. The absolute value ensures a positive distance.

Total outcomes = product of choices at each step (Fundamental Counting Principle).