For C = 40 + 0.8y ; the value of multiplier is :

5

The correct answer is option (1) : 5

The multiplier (k) is calculated using the formula :

$k=\frac{1}{1-MPC}$

where MPC is the marginal propensity to consume.

In the given consumption function C = 40 + 0.8y, the marginal propensity to consume (MPC) is 0.8.

$k= \frac{1}{1-0.8}=\frac{1}{0.2}= 5 $