Writing & Evaluating Variable Expressions Chapter 1-3 Pre-Algebra Prentice Hall

Evaluation Variable Expressions To evaluate a variable expression, you first replace each variable with a number. Than, you use the order of operations to simplify the expression. Evaluate: 4y − 15 for y = 9 ◦ First replace the variable y with number 9 ◦ 4∙9 − 15 ◦ Than use order of operation to simplify: ◦ 36 − 15 = 21

Quick Check Evaluate each expression. 1. 6(g + h), for g = 8 and h =7 ◦ xy – z, for x = 4, y = 3, z = 1 ◦ for r = 13, and s = 11 ◦ 12

Purchasing Problem Example Energy drinks come in cases of 24 bottles. a)Write a variable expression for the number of cases a store should order to get b bottles of energy drinks. b)Evaluate the expression for 120 bottles. ← bottles wanted ← number in case Evaluate for b = 120 cases

Exercises 1. ◦ ◦ ◦ ◦ ◦2◦2

Problems 1. Write an expression for the number of kilometers a dolphin travels in d hours swimming at 8km/h. Then find the number of kilometers the dolphin travels in 3 hours ◦ 8d 24 km 2. A fitness club requires a $100 initiation fee and dues of $25 each month. Write an expression for the cost of membership for n months. Then find the cost of membership for one year. ◦ n $400