Algebraic Expressions & Equations

Adult Ideal Weight

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Adult Ideal Weight

Use this rule of thumb: an adult’s ideal weight in kilograms is 100 less than his or her height in centimeters.

  • Let h = an adult’s height in centimeters. Write an algebraic expression for the person’s ideal weight in kilograms. Evaluate your expression to find the ideal weight, in kilograms, for an adult who is 150 cm tall.
  • Write and solve an equation to find the height, in centimeters, of an adult who has an ideal weight of 30 kg.


  • An algebraic expression can combine arithmetic operations, numbers, and letters. Letters are used to represent variables. These are examples of algebraic expressions that contain variables: a , 3b , and 4x + 5. The variables in the expressions area ,b , andx .
  • To evaluate an algebraic expression, replace each variable in the expression with a number and find the value of the expression. For example, to evaluate the expression 4 x + 5 whenx = 7, replacex with 7 and find the value of 4 • 7 + 5, which is 28 + 5, or 33
  • An equation is a statement where two expressions are equal. It is formed by placing an equals sign between the two equivalent expressions
  • To solve an equation, find the value of the variable that makes the equation true.