Answer: 2/3
Explanation: Crowding out may described as an effect which stems from government involvement in an economic market resulting in the reduction of personal consumer goods or investments and businesses due to rising interest rates and low capital accumulation.
In the question above, if crowding out is ignored, The marginal propensity to consume(MPC) will be:
Multiplier = $30 billion ÷ $10 billion = 3
Multiplier = 1÷ (1 - MPC)
3 = 1 ÷ (1 - MPC)
3(1 - MPC) = 1
3 - 3MPC = 1
-3MPC = 1-3
-3MPC = - 2
MPC = 2/3