National income $=1000$
Autonomous consumption expenditure $=200$
Investment expenditure $=100$
National Income $=$ Consumption + Investment Expenditure
$\mathit{Y}=\overline{\mathit{c}}+\mathit{c}\mathit{Y}+\mathit{I}$
$1000=200+\mathit{c}\left(1000\right)+100$
$1000=300+\mathit{c}\left(1000\right)$
$1000-300=\mathit{c}\left(1000\right)$
$700=\mathit{c}\left(1000\right)$
$\mathit{c}=\frac{700}{1000}$
$\mathit{c}=0.7$
Marginal propensity to consume $=0.7$ .