Exercise 40 Page 234

Let M be the amount of money Ivan has. He can buy 12 CDs. If a CD costs $ x, then we have the following equation. M= 12 x However, Ivan could buy 2 more CDs, if the cost of each CD was $0.2 less. That is, Ivan could buy 14 CDs, if the cost of each CD was $( x-0.2). The amount of money Ivan has is M. Therefore, we can write the following. M= 14( x-0.2) We have two equations and two unknowns so we can find M and x.

M=12x & (I) M=14(x-0.2) & (II)

Substitute

(II): M= 12x

M=12x 12x=14(x-0.2)

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(II): Solve by substitution

Distr

(II): Distribute 14

M=12x 12x=14x-2.8

SubEqn

(II): LHS-14x=RHS-14x

M=12x - 2x=- 2.8

DivEqn

(II): .LHS /(- 2).=.RHS /(- 2).

M=12x x=1.4

Now that we've found that x=1.4, we can use this to solve for M in the first equation.

M=12x x=1.4

Substitute

(I): x= 1.4

M=12( 1.4) x=1.4

Multiply

(I): Multiply

M=16.8 x=1.4

Ivan has $ 16.80 which is option A.