## Precalculus (6th Edition) Blitzer

Published by Pearson

# Chapter 8 - Section 8.1 - Matrix Solutions to Linear Systems - Exercise Set - Page 895: 50

#### Answer

The number of rooms, bathrooms, fireplaces, and elevators are $132,35,28,3$ respectively.

#### Work Step by Step

Step 1. Assume the number of rooms, bathrooms, fireplaces, and elevators are $w,x,y,z$ respectively. Step 2. Based on the given conditions, we have $\begin{cases} w+x+y+z=198 \\ w-x-y=69 \\ y-z=25 \\ 2x-y-z=39 \end{cases}$ Step 3. Adding up the last two equations, we have $2x-2z=64$ or $x=z+32$ and the third equation gives $y=z+25$ Step 4. Substituting $x=z+32$ and $y=z+25$ in the first and second equations, we have $\begin{cases} w+z+32+z+25+z=198 \\ w-z-32-z-25=69 \end{cases}$ or $\begin{cases} w+3z=141 \\ w-2z=126 \end{cases}$ Step 5. Taking the difference of the two equations, we get $5z=15$ thus $z=3$ Step 6. Back-substitute to get $w=126+2(3)=132$, $x=35, y=28$ Step 7. Thus, the number of rooms, bathrooms, fireplaces, and elevators are $132,35,28,3$ respectively.

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.