Questions: Suppose C = 25y + 10 and y=30 x+15.
Which of the following is equivalent to C=25 y+ 10, but written only in terms of x ?
a.) C=75 x+45
b.) C=750 x+375
c.) C=750 x+385
d.) C=75 x+385
Transcript text: 13:22
30
Question
Tutorials
5 - Substitution in Multi-Step Linear Equations
LEARNING OBJECTIVE: Use the Substitution Property of Equality to rewrite an expression for another variable.
Suppose C = 25y + 10 and $y=30 x+15$.
Which of the following is equivalent to $\mathrm{C}=25 \mathrm{y}+$ 10, but written only in terms of $x$ ?
a.) $C=75 x+45$
b.) $C=750 x+375$
c.) $C=750 x+385$
d.) $C=75 x+385$
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Solution
Solution Steps
To solve this problem, we need to substitute the expression for \( y \) into the equation for \( C \). Given \( C = 25y + 10 \) and \( y = 30x + 15 \), we can replace \( y \) in the first equation with \( 30x + 15 \). Then, we simplify the resulting expression to find \( C \) in terms of \( x \).
Step 1: Substitute \( y \) in the equation for \( C \)
We start with the equations:
\[
C = 25y + 10
\]
and
\[
y = 30x + 15.
\]
Substituting \( y \) into the equation for \( C \):
\[
C = 25(30x + 15) + 10.
\]
Step 2: Simplify the expression
Now, we simplify the expression:
\[
C = 25 \cdot 30x + 25 \cdot 15 + 10.
\]
Calculating each term:
\[
C = 750x + 375 + 10.
\]
Combining the constant terms:
\[
C = 750x + 385.
\]
Step 3: Identify the equivalent expression
We have derived that:
\[
C = 750x + 385.
\]
Now, we compare this with the given options: