Q.Explain, with an example, how a stock variable and its corresponding flow variable are related to each other.

A stock at any date is the accumulated result of the flows that have occurred up to that date, so the two are always linked even though they are measured differently. …

A stock and its corresponding flow are two sides of the same underlying quantity, viewed differently in time:

• A stock is like a photograph — it captures the quantity at one instant.
• A flow is like a video — it captures how the quantity changes over an interval.

Example — Wealth and Saving: a household's wealth (stock) at the end of a year equals its wealth at the start of the year, plus whatever part of the year's income (flow) it did not consume, i.e., its saving during the year:

Similarly, Capital (stock) at the end of the year equals capital at the start of the year plus Investment (flow) during the year — investment is precisely defined as the addition made to the capital stock during a period:

$\text{Capital}_{end} = \text{Capital}_{start} + \text{Investment during the year}$ …

Describing stock and flow only in the abstract ('one has a time dimension, the other doesn't') without showing the numerical/relational link between a specific stock and its own corresponding flow — a full-mark a …