Tamil Nadu HSE First Year Economics common mistakes
Tamil Nadu HSE First Year Economics · Understand the traps and how to avoid them.
Writing that a change in price of the good itself causes a shift of the demand curve, instead of a movement along it.
Students memorise "increase in demand = curve shifts right" without separating the two causes of a demand change; they treat any change in quantity demanded as a shift.
What to do instead
Drill the rule as a two-column table: own-price change → movement along the curve (expansion/contraction); income, tastes, prices of related goods, expectations, population → shift (increase/decrease). Practise with five one-line scenarios and label each as movement or shift before drawing anything.
Defining elasticity of demand as an absolute change (ΔQ) rather than a ratio of percentage changes, and reporting a value greater than 1 for a steep curve without computing it.
The formula is remembered loosely as "change in quantity over change in price", and students skip the percentage step because it looks like extra work.
What to do instead
Always write the full formula first: Ed = (% change in quantity demanded) ÷ (% change in price). Work two numericals end to end - one with a price fall, one with a price rise - and state whether demand is elastic, inelastic or unitary with the reason. Remember Ed is negative by convention but reported as a positive number.
Confusing the short-run and long-run cost curves, or drawing the average cost curve as U-shaped without explaining why it falls and then rises.
The law of variable proportions and returns to scale are studied in separate chapters, so students do not connect diminishing marginal returns (short run, one fixed factor) with the shape of AC and MC.
What to do instead
Build one diagram with MC cutting AC at its minimum, and write beside it: AC falls while MC < AC, rises while MC > AC. Then state in one sentence that the short-run U-shape comes from the law of variable proportions, while long-run economies and diseconomies of scale explain the long-run curve.
Treating perfect competition and monopoly as differing only in the number of firms, and asserting that a monopolist can charge any price it likes.
Feature tables are memorised row by row without the underlying idea that market power depends on the elasticity of the firm's demand curve and on entry barriers.
What to do instead
For each market form write three linked facts: number of sellers, nature of the product, and conditions of entry - then derive the demand curve (horizontal for a competitive firm, downward-sloping for a monopoly). Add the correction that a monopolist is a price maker but still constrained by demand, and cannot sell more only by lowering price.
Stating that rent, wages, interest and profit are determined by supply alone, or by demand alone, instead of by the interaction of derived demand and factor supply.
Factor pricing is taught quickly at the end of the year, and students carry over the product-market habit of looking for a single determinant.
What to do instead
Use the marginal productivity theory as the frame: demand for a factor is derived from demand for the good and depends on marginal revenue product; supply depends on the factor owner's choice between work and leisure (or saving and consumption). Write the equilibrium condition MRP = MFC for each factor and note the special case of land, whose supply is nearly fixed.
Counting transfer payments, the sale of second-hand goods, or intermediate goods in national income, and double-counting the value of flour inside the price of bread.
The distinction between final and intermediate goods and between factor and transfer income is abstract, and students apply everyday intuition that "all money spent in the economy counts".
What to do instead
Keep a running exclusion list - intermediate goods, second-hand sales, transfer payments, financial transactions, illegal output - and test every item against two questions: was anything new produced this year, and is this payment a reward for a factor of production? Practise the value-added method on a three-stage example (wheat → flour → bread) to see why only the sum of values added is counted.
Mixing up GNP at market price, NNP at factor cost (national income) and per capita income, and applying the wrong adjustment when converting between them.
The chain of adjustments - depreciation, net factor income from abroad, indirect taxes minus subsidies - is long, and students apply them in the wrong order or forget one.
What to do instead
Write the ladder once and reuse it: GDP at MP − depreciation = NDP at MP; NDP at MP − net indirect taxes = NDP at FC; add net factor income from abroad to move from domestic to national. Then define national income as NNP at FC and per capita income as national income ÷ population, and solve one full numerical using the ladder step by step.
Describing the money multiplier as if banks lend out the whole deposit, and failing to separate the reserve ratio from the credit-creation limit.
The phrase "banks create credit" is memorised as a slogan, and the arithmetic of required reserves is treated as a separate topic rather than the mechanism itself.
What to do instead
Work a numerical: with a cash reserve ratio of 10%, a fresh deposit of ₹1,000 supports total credit of ₹1,000 ÷ 0.10 = ₹10,000. Show the first three rounds of lending explicitly, then state the formula as 1/CRR. Add that the multiplier is an upper limit, weakened by cash leakage and excess reserves held by banks.
Answering Indian economy questions with generic statements ("poverty is a problem", "agriculture is important") rather than naming the specific scheme, indicator or Tamil Nadu feature the question asks about.
This section rewards current, local knowledge, but students revise it last and rely on general awareness instead of learning named programmes, their launch years and their objectives.
What to do instead
Maintain a one-page fact sheet organised by theme - poverty and employment programmes, food security, irrigation and crop patterns, industrial corridors and SEZs in Tamil Nadu, state human development indicators - with the name, year and one-line purpose for each. Answer in the pattern: name it, date it, state its objective, then give one concrete outcome.
Computing mean, median and mode correctly but misreading a table - using the wrong column, ignoring class intervals in grouped data, or reporting the mean without units - and drawing a graph without labelling the axes.
Statistical method is treated as arithmetic practice, so the step of reading the question and setting out the data is skipped under time pressure.
What to do instead
Adopt a fixed routine for every statistics numerical: copy the data into a clean table, write the formula, substitute, compute, then state the answer with its unit and check whether the mean lies between the minimum and maximum. For grouped data, write the class midpoints (m) before multiplying by frequency. Always label both axes and give the diagram a title.