Textbook Problem

Modeling Data The table shows the net sales x (in billions of dollars), the total assets y (in billions of dollars), and the shareholder’s equity z (in billions of dollars) for Walmart for the years 2010 through 2015. (Source: Wal-Mart Stares, Inc. )

Year	2010	2011	2012	2013	2014	2015
x	405.0	418.5	443.4	465.6	473.1	482.2
y	170.7	180.8	193.4	203.1	204.8	203.7
z	70.7	68.5	71.3	76.3	76.3	81.4

A model for the data is $z=f\left(x,y\right)=0.428x-0.653y+\mathrm{8.172.}$

(a) Complete a fourth row in the table using the model to approximate z for the given values of x and y. Compare the approximations with the actual values of z.

(b) Which of the two variables in this model has more influence on shareholder’s equity? Explain.

(c) Simplify the expression for f(x, 150) and interpret its meaning in the context of the problem.