Marginal Propensity to Save

Suppose C$($x$)$ measures an economy's personal consumption expenditure and x the personal income, both in billions of dollars. Then the following function measures the economy's savings corresponding to an income of x billion dollars.

S$($x$)=$ x $-$ C$($x$)($income minus consumption$)$

The quantity

dSdx

below is called the marginal propensity to save.

dSdx

$=1$

dCdx

For the following consumption function, find the marginal propensity to save when x $=5.($Round your answer to three decimal places.$)$

C$($x$)=0\mathrm{.}875$x$1\mathrm{.}1+15\mathrm{.}6$

$ billion per billion dollars