General Science
Mohs Hardness Mnemonic — "The Girls Can Fight And Other Queer Things Can Do" for Talc(1), Gypsum(2), Calcite(3), Fluorite(4), Apatite(5), Orthoclase(6), Quartz(7), Topaz(8), Corundum(9), Diamond(10). Essential for identifying minerals by scratch test.
pH Scale Memory — pH < 7 = Acidic (think "A" comes before 7), pH = 7 = Neutral, pH > 7 = Basic. Lemon juice ~2, Vinegar ~3, Pure water 7, Baking soda ~9, Bleach ~13.
VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, Red for visible light spectrum in increasing wavelength order. Reverse for decreasing energy: ROY G BIV.
Mitosis Phases — "I Picked My Apples Today" for Interphase, Prophase, Metaphase, Anaphase, Telophase. Chromosomes align at metaphase, separate at anaphase.
Reactivity Series Trick — "Please Send Charlie's Monkeys And Zebras In Lead Cages Having Secure Guards" for Potassium, Sodium, Calcium, Magnesium, Aluminum, Zinc, Iron, Lead, Copper, Mercury, Silver, Gold (decreasing reactivity).
Indian Economy
Five-Year Plan Periods — 1st Plan started 1951; each plan = 5 years. Quick math: 1951 + 5n gives you nth plan start year until 2017 when NITI Aayog replaced Planning Commission.
Repo vs Reverse Repo — Repo = RBI Repurchases from banks (banks borrow); Reverse Repo = banks deposit with RBI. Repo rate > Reverse repo rate always.
Direct vs Indirect Tax — Direct tax: paid TO government by the SAME person (income tax). Indirect: paid BY someone else TO government (GST). Cannot shift direct tax burden.
Mental Ability
Compass Rotation Trick — Draw NEWS cross; clockwise 90° rotations: N→E→S→W→N. For left/right turns: person faces direction, then turn accordingly. Always sketch compass for complex problems.
Blood Relations Gender — Father's/Mother's brother = Uncle; Father's/Mother's sister = Aunt. Brother's/Sister's son = Nephew; Brother's/Sister's daughter = Niece. Maternal = mother's side, Paternal = father's side.
Coding Pattern Detection — Check alphabet position shifts first (A=1, Z=26). Common patterns: +1, -1, reverse position (A↔Z), positional value multiplication, or vowel-consonant swaps.
Syllogism Euler Circles — Draw overlapping circles for premises. Universal affirmatives (All A are B) = A inside B. Negatives (No A are B) = separate circles. Test conclusions by drawing all possibilities.
Direction Distance Net Displacement — North-South movements = vertical, East-West = horizontal. Final position: Pythagoras (x²+y²) for distance, tan⁻¹(y/x) for direction. Sketch always helps.
Arithmetic
Divisibility by 11 — Alternating sum trick: subtract odd-position digits from even-position digits. If result = 0 or divisible by 11, original number is divisible by 11. E.g., 121: (1+1)-2=0 ✓
Divisibility Quick Rules — By 3: sum of digits divisible by 3. By 4: last 2 digits divisible by 4. By 8: last 3 digits divisible by 8. By 9: digit sum divisible by 9.
Percentage-Fraction Equivalents — 50%=½, 33.33%=⅓, 25%=¼, 20%=⅕, 10%=1/10, 12.5%=⅛, 16.67%=⅙. Memorize these for instant conversion and faster mental calculation in exams.
Profit/Loss Shortcut — If CP=100, SP=selling price directly gives profit%. If SP=100, CP=100×100/(100+profit%). For 2 successive discounts d₁%, d₂%: net = d₁+d₂-(d₁×d₂/100).
Average Addition Trick — When nth item added, new average = old average + (new value - old average)/n. Saves recalculation time. For weighted average: multiply each value by weight, sum, divide by total weight.
HCF-LCM Product Rule — For two numbers: HCF × LCM = Product of the two numbers. If HCF and one number known, find other number instantly.
Area Formulas Mnemonic — Triangle = ½bh; Circle = πr²; Rectangle = lb; Square = a²; Trapezium = ½(sum of parallel sides)×height. Remember π ≈ 22/7 ≈ 3.14.
English Language
FANBOYS Conjunctions — For, And, Nor, But, Or, Yet, So. These coordinate conjunctions join independent clauses; use comma before them in compound sentences.
Active-Passive Voice Swap — Subject↔Object swap; verb becomes "be + past participle." Active: "Ram eats rice" → Passive: "Rice is eaten by Ram." Tense of 'be' matches original verb tense.
Spotting Subject-Verb Errors — Singular subjects take singular verbs (is, was, has); plural take plural verbs (are, were, have). Ignore intervening phrases: "The box of chocolates IS expensive."
Common Homophones — Their/There/They're; Your/You're; Its/It's; Affect(verb)/Effect(noun); Principal(main)/Principle(rule); Compliment(praise)/Complement(complete). Mark these in error-spotting questions.