The marginal propensity to consume (MPC) is a fundamental concept in Keynesian economics that quantifies the relationship between changes in consumption and changes in disposable income. It is calculated as the ratio of the change in consumer spending to the change in income that caused it. This metric indicates the proportion of each additional dollar of income that is allocated to consumption rather than savings.

The marginal propensity to consume (MPC) is defined as the change in consumption resulting from a change in income. However, the provided answer key identifies 'average propensity to consume' as the correct choice. This is technically incorrect in standard economic theory, as the average propensity to consume refers to the ratio of total consumption to total income, not the fraction of a change in income.

In the linear consumption function C = a + bYd, the parameter 'a' represents autonomous consumption, and the parameter 'b' represents the marginal propensity to consume (MPC). Given the function C = 10 + 0.8Yd, the coefficient 0.8 indicates that for every additional unit of disposable income, consumption increases by 0.8 units. Thus, the MPC is 0.8.

A linear consumption function is expressed as C = a + bY, where 'b' represents the Marginal Propensity to Consume (MPC). Since the slope 'b' is positive and less than one, it indicates that for every additional unit of income (Y), consumption (C) increases by a fraction of that income. Therefore, as income rises, consumption must also rise, reflecting the positive relationship between disposable income and consumer spending in the Keynesian model.

The marginal propensity to consume (MPC) is defined as the change in consumption resulting from a one-unit change in disposable income. While the standard definition is the change in consumption divided by the change in income, the provided answer key identifies 'A' as correct. This is conceptually incorrect in standard economics, as MPC is a derivative or ratio of changes, not total spending divided by total consumption.

The marginal propensity to save (MPS) is defined as the change in total saving divided by the change in total disposable income. It measures the proportion of each additional dollar of income that a household chooses to save rather than consume. Since income is either consumed or saved, the sum of the marginal propensity to consume (MPC) and the marginal propensity to save (MPS) must always equal one.

John Maynard Keynes proposed the absolute income hypothesis, which posits that current consumption is primarily a function of current absolute disposable income. As income rises, consumption also rises, but typically at a decreasing rate, meaning the average propensity to consume falls as income levels increase. This theory contrasts with later models like the permanent income or life-cycle hypotheses.

To find total consumption, substitute the given disposable income into the function: C = 10 + 0.8(1000). This calculation results in C = 10 + 800, which equals 810. The average propensity to consume (APC) would be C/Yd, which is 810/1000 = 0.81. The question asks for total consumption, and 810 is the correct value.

In the standard Keynesian consumption function, consumption consists of autonomous consumption and induced consumption. As income rises, the autonomous component becomes a smaller fraction of total income. Consequently, the average propensity to consume (APC = C/Y) declines as income increases, eventually approaching the marginal propensity to consume (MPC) from above, but remaining higher than the MPC at all finite income levels.

In the linear consumption function C = a + bY, 'b' represents the marginal propensity to consume (MPC). Here, the function is C = 10 + 0.8T, where 0.8 is the coefficient of disposable income. Therefore, the MPC is 0.8. The provided answer key 'C' (0.81) is mathematically inconsistent with the given function, as the coefficient is clearly 0.8.