what is meant by investment multiplier explain the relationship between marginal propensity to consume and investment multiplier 

Investment multiplier or simply 'multiplier' implies that any change in the investment leads to a corresponding change in the income and output by multiple times. That is, in other words, the change in the income and output is more than (or multiple times of) the change in investment. The concept of investment multiplier can be explained with the help of the following diagram.

In the above diagram, AD is the initial Aggregate Demand curve. Point E is the initial equilibrium point, where the aggregate demand curve intersects the 45° income-line. OY is the equilibrium level of income. Now suppose the level of investment increases. With this the Aggregate Demand curve shifts parallely upwards to AD'. The new equilibrium is established at point E' and correspondingly the equilibrium income and output increases from OY to OY´. The increase in the income and output (∆Y) is greater than the increase in the investment (∆I).

Relationship between marginal propensity to consume and  and investment multiplier:

There is a direct relationship between multiplier and MPC. Higher the value of MPC, higher the multiplier and vice versa. Multiplier is also estimated with reference to MPC as under:
                         K = 1/1-MPC
This equation establishes a direct relationship between MPC and K.
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