The number of times by which income increases as a result of increase in investment is called investment multiplier. Investment multiplier shows a relationship between initial increment in investment and the resulting increment in national income. $K\;=\;\frac{\Delta Y}{\Delta I}$where $K\;=\;\text{ multiplier }\;$ $\Delta Y\;=\;\text{ change in income }\;$ $\Delta I\;=\;\text{ change in investment }\;$Relation of multiplier with MPC : $\;K=\;\frac{\Delta Y}{\Delta I}$ $\;K=\;\frac{\Delta Y}{\Delta C}$(Dividing this equation by $\Delta Y$ we get) $K\;=\;\frac{\Delta Y}{\Delta Y-\Delta C}$ $\;=\;\frac{\;\frac{\Delta Y}{\Delta Y}}{\frac{\Delta Y}{\Delta Y}-\;\frac{\Delta C}{\Delta Y}} = \;\frac{1}{1-MPC}$ There is a direct relation between $K$ and MPC. If MPC is high, K will also be high but if MPC is low $K$ will also be low.