Maharashtra SSC Workshop Science & Calculation ITI common mistakes
Maharashtra SSC Workshop Science & Calculation ITI · Understand the traps and how to avoid them.
When converting a fraction such as 7/16 to a decimal, candidates divide 16 by 7 (getting about 2.29) instead of dividing the numerator by the denominator, then carry that wrong value into the percentage or ratio question that follows.
The layout of a fraction is not read as a division instruction; candidates memorise 'divide the two numbers' without fixing the order, and under time pressure they grab the numbers in the order they appear on the page.
What to do instead
Drill the rule 'top divided by bottom' with the mnemonic that the fraction bar is a division sign with the numerator on top. Practise ten conversions (7/16, 5/8, 3/32, 9/20) and check each by multiplying the answer back by the denominator to recover the numerator.
In percentage problems, candidates apply the percentage to the wrong base - for example adding a 20% mark-up to a cost and then taking 20% off the marked price and claiming the original cost is recovered.
The words 'of', 'on' and 'by' are skimmed, and candidates treat percentage change as symmetric because addition and subtraction feel reversible.
What to do instead
Always write the base explicitly before calculating ('20% of cost', '20% of marked price'). Work the classic 100 → +20% → 120 → −20% → 96 example once by hand so the asymmetry is seen numerically, then apply the same explicit-base habit to ratio and proportion questions.
Mixing units inside one mensuration formula - substituting a diameter in millimetres with a length in metres into the cylinder volume formula, or using radius where the formula needs diameter.
Formulas are memorised as letter strings (V = πr²h) without the habit of listing given quantities with units first, and 'diameter' is read as 'radius' because both appear in the same chapter.
What to do instead
Before substituting, write a data line: 'd = 50 mm → r = 25 mm; h = 0.2 m → 200 mm'. Convert everything to one unit, then substitute. Memorise the paired forms (V = πd²h/4) so diameter can be used directly without a conversion slip.
Using the wrong trigonometric ratio for a right-triangle workshop problem, for example using sine when the known side is adjacent to the angle, or forgetting to press the inverse function when the angle is the unknown.
SOH-CAH-TOA is recalled as a chant but not linked to which sides are actually named in the diagram, and calculator work is done without checking whether degrees or radians mode is active.
What to do instead
Label the triangle's three sides as opposite, adjacent and hypotenuse relative to the marked angle before choosing a ratio. Then write the equation with the unknown isolated before touching the calculator. Check the mode: sin 30 must give 0.5, and if it does not the calculator is in radian mode.
Confusing mass, weight and density - treating a density in g/cm³ as if it were a weight, or using density × volume and reporting the answer in newtons.
Everyday language uses 'weight' for mass, and the formula triangle (m = ρV) is memorised without units attached, so the output unit is never considered.
What to do instead
Attach units to every symbol: ρ in g/cm³, V in cm³, m in g. Do one conversion deliberately (1 g/cm³ = 1000 kg/m³) and one contrast problem: mass of a 200 cm³ steel block (ρ = 7.8 g/cm³) versus its weight (× 9.81). State the unit in the final answer line every time.
In cutting-speed calculations, candidates substitute the tool diameter in millimetres directly into N = 1000V/(πD) but forget the 1000, or use the radius instead of the diameter, producing an RPM that is out by a factor of 1000 or 2.
The formula is learned as a shape without understanding that the 1000 converts metres to millimetres, and diameter and radius are used interchangeably from mensuration practice.
What to do instead
Derive it once: V (m/min) × 1000 = πDN with D in mm. Then do a sanity check - a 50 mm drill at 25 m/min should give roughly 160 rpm, not 1.6 or 160 000. If the answer is wildly off, the 1000 or the diameter is the suspect.
Computing machining time as length divided by feed without converting feed per revolution into feed per minute, or ignoring the approach and over-travel allowance.
Feed is quoted in mm/rev on the machine but time needs mm/min, and the formula T = L/(f × N) is memorised without the N term being understood as the rev/min conversion.
What to do instead
Write the chain explicitly: feed per minute = f (mm/rev) × N (rev/min); T = (L + approach + over-travel)/feed per minute. Work one example with all terms visible, then check the units cancel to minutes before trusting the number.
In gear and screw-thread problems, candidates mix module with diametral pitch, or use the pitch diameter instead of the outside diameter when computing the blank size for a gear.
Both module and diametral pitch describe tooth size, and the several gear diameters (pitch, outside, root) are learned as a list rather than as related quantities.
What to do instead
Fix the metric relations firmly: module m = PCD/N, and outside diameter = m(N + 2). For threads, pitch = 1/threads per inch for imperial and is given directly for metric. Do a paired problem in both systems and convert one to the other to see where the factors of 25.4 belong.
Treating temperature difference and absolute temperature as interchangeable in heat calculations, or mixing heat units - using °C in a formula that expects kelvin, or confusing kcal with kJ.
The Celsius and kelvin scales share a degree size, so candidates assume the numbers can be swapped, and heat quantity units look similar on the page.
What to do instead
Adopt the rule: temperature differences may be used in °C or K interchangeably, but absolute temperatures in gas or radiation formulas must be in kelvin (K = °C + 273). Write the unit of every intermediate result and use 1 kcal = 4.187 kJ explicitly when converting.
Describing a material property with the wrong term - calling a hardened steel 'ductile', calling cast iron 'malleable' in its normal form, or confusing hardness with toughness when answering a properties question.
The property words are learned as a vocabulary list without a physical picture, and several of them (strength, hardness, toughness) are used loosely in everyday speech.
What to do instead
Anchor each term to a test or behaviour: hardness resists indentation (Brinell/Rockwell), toughness resists shock without fracture (Izod), ductility allows drawing into wire (percentage elongation). Build a short table of five common materials against these three properties and revise it before the exam.