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U Substitution Homework Key Classzone

7.2 Problem Solving Help

Help for Exercises 29-31 on page 400

In Exercise 29, you are asked to find the value of two unknown quantities: the number of 11-inch softballs and the number of 12-inch softballs. You should be able to determine these two equations from the verbal models given below.

Verbal Models for Exercise 29:

   

   

Assign variables to each unknown quantity. Then write and solve an algebraic system of equations (using the substitution method), and check your answer.

In Exercise 30, apply the formula for the perimeter of a rectangle,
. You already know the value of P and you have expressions for the length and width in a single variable. Because of this, you do not need to solve a system of equations. Make sure that your answer includes units.

Exercise 31 can be approached with the verbal models shown below. The unknowns are the cost of each stock.

Verbal Models for Exercise 31:

   

   

В окружающей ее тишине не было слышно ничего, кроме слабого гула, идущего от стен. Гул становился все громче. И вдруг впереди словно зажглась заря. Темнота стала рассеиваться, сменяясь туманными сумерками. Стены туннеля начали обретать форму.