Final answer:
In the Keynesian-cross model, prices and wages are assumed constant in the short run, leading to changes in output without affecting prices, as per the Expenditure Multiplier concept.
Step-by-step explanation:
In the Keynesian-cross model, prices and wages are assumed to be constant to illustrate the short-run case. This model highlights how, in the short run, shifts in aggregate demand can lead to changes in output and employment levels without affecting prices. This assumption of fixed prices and wages results in a flat short-run aggregate supply (SRAS) curve below potential GDP, as shown in various figures relating to Keynesian economics. The Expenditure Multiplier is also a key concept in this model, emphasizing the impact of changes in aggregate expenditure on the overall level of output or national income.