Final answer:
Contractionary monetary policy, which tightens the money supply, raises interest rates, reduces borrowing, and shifts aggregate demand leftward, would lead to an increase in real interest rates and a decrease in output in the Keynesian short-run model.
Step-by-step explanation:
If the government decided to tighten monetary policy and decrease government expenditures, in the short run in the Keynesian model, the effect of these policies would be to raise the real interest rate and decrease the level of output. Contractionary monetary policy causes the supply of money and credit in the economy to decrease, which raises the interest rate, discourages borrowing for investment and consumption, and shifts aggregate demand to the left. The combination of these effects would result in a lower price level and a decrease in real GDP, at least in the short run.