BSF HC RO/RM cheat sheet
BSF HC RO/RM · Keep the key ideas within reach.
General Intelligence and Reasoning
Letter positions: A=1 … Z=26; reverse position = 27 − forward position (A↔Z, M↔N).
Opposite-letter pairs (sum 27): AZ, BY, CX, DW, EV, FU, GT, HS, IR, JQ, KP, LO, MN.
Coding-decoding: test shift (+n/−n), reversal, then position-sum tricks; verify one letter before applying to all.
Series rule order: check differences, then ratios, then alternating/prime/square patterns, then two interleaved series.
Odd pair out: compare letter-position differences; a valid pair usually keeps equal gap (e.g., 3 and 3).
Blood relations: draw a tree; vertical = parent/child, horizontal = spouse/sibling; never assume gender from a name.
Direction sense: use N-up, E-right grid; net displacement = √(x² + y²), direction from sign of x and y.
Syllogism: valid only if conclusion holds in every possible Venn diagram; 'some' is reversible, 'all' is not.
Seating arrangement: fix the most constrained person first, then place left/right from that person's facing direction.
Elementary Mathematics
Average = sum ÷ count; new average after adding x: (old sum + x) ÷ (n + 1).
Percentage change = (new − old)/old × 100; successive changes a% then b%: net = a + b + ab/100.
Simple interest = PRT/100; Compound amount = P(1 + R/100)^T; CI − SI for 2 years = P(R/100)².
Profit% = (SP − CP)/CP × 100; discount% is always on marked price, profit% always on cost price.
Speed conversion: 1 km/h = 5/18 m/s; time = distance ÷ speed; relative speed adds when moving opposite, subtracts when same direction.
Work: if A takes a days and B takes b days, together = ab/(a + b) days; use 1/a + 1/b = 1/together.
Ratio and mixture: alligation - ratio of quantities = (mean − cheaper) : (dearer − mean).
Mensuration: circle area πr², circumference 2πr; cylinder volume πr²h, curved surface 2πrh; sphere volume 4/3 πr³.
LCM × HCF = product of the two numbers; for fractions, LCM = LCM of numerators ÷ HCF of denominators.
General Awareness and General Knowledge
Indian Constitution: adopted 26 November 1949, came into force 26 January 1950; Dr B. R. Ambedkar chaired the Drafting Committee.
Fundamental Rights (Part III) are enforceable in courts; Fundamental Duties (Part IVA, Article 51A) were added by the 42nd Amendment, 1976.
President is elected by an electoral college; Supreme Court judges retire at 65, High Court judges at 62.
Border guarding: BSF (1965) guards land borders with Pakistan and Bangladesh; ITBP guards the China border; Assam Rifles guards Myanmar border.
BSF motto 'Jeevan Paryant Kartavya'; BSF comes under the Ministry of Home Affairs; Assam Rifles under Ministry of Home Affairs with operational control of Army.
National symbols: tiger (animal), peacock (bird), lotus (flower), mango (fruit), Ganga (river), 'Jana Gana Mana' (anthem, Rabindranath Tagore).
Space and defence: ISRO HQ Bengaluru; Chandrayaan-3 landed near lunar south pole in August 2023; BrahMos is a supersonic cruise missile.
Geography: Tropic of Cancer passes through 8 Indian states; longest river Ganga; Deccan Plateau lies between Western and Eastern Ghats.
Static science: unit of force newton, power watt, frequency hertz; speed of light ≈ 3 × 10⁸ m/s; sound cannot travel in vacuum.
English Language and Comprehension
Subject-verb agreement: singular subject takes singular verb; 'one of the + plural noun' takes a singular verb.
Articles: 'a' before consonant sound, 'an' before vowel sound (an hour, a university); 'the' for unique or already specified nouns.
Prepositions of time: in (months/years), on (days/dates), at (clock time); since + point of time, for + duration.
Active to passive: object becomes subject, verb becomes be + past participle, agent introduced by 'by'.
Direct to indirect: shift tense one step back; change pronouns by 1st→speaker, 2nd→listener, 3rd→unchanged; today→that day.
Common error traps: 'discuss about' (drop about), 'married with' (use to), 'comprises of' (drop of), 'senior than' (use to).
Synonyms/antonyms are best solved by placing the word in context; idioms like 'at the drop of a hat' = instantly.
Cloze and comprehension: read the whole passage first, then answer only from stated facts, not outside knowledge.
One-word substitutions: 'one who speaks many languages' = polyglot; 'fear of water' = hydrophobia; 'government by the people' = democracy.
Hindi Language and Comprehension
संधि: स्वर संधि (दो स्वर मिलें), व्यंजन संधि (व्यंजन+स्वर), विसर्ग संधि; जैसे विद्या + आलय = विद्यालय (दीर्घ संधि)।
समास: तत्पुरुष (अंतिम पद प्रधान), द्वंद्व (दोनों प्रधान), बहुव्रीहि (तीसरा अर्थ प्रधान), द्विगु (संख्या सूचक)।
उपसर्ग अर्थ बदलते हैं (अ + सत्य = असत्य); प्रत्यय से नए शब्द बनते हैं (लड़क + पन = लड़कपन)।
पर्यायवाची: पानी - जल, नीर, वारि; आग - अग्नि, अनल, पावक; पृथ्वी - धरती, भूमि, वसुधा।
विलोम: अंधकार × प्रकाश, उत्थान × पतन, सजीव × निर्जीव, आदि × अंत।
मुहावरे अर्थ सहित: 'नौ दो ग्यारह होना' = भाग जाना; 'आँख का तारा' = बहुत प्यारा; 'लोहे के चने चबाना' = कठिन काम करना।
कारक चिह्न: कर्ता 'ने', कर्म 'को', करण 'से/के द्वारा', संप्रदान 'के लिए', अपादान 'से', अधिकरण 'में/पर'।
वाक्य शुद्धि: लिंग, वचन और कारक की संगति जाँचें; अनावश्यक 'को' और 'ने' हटाएँ।
रस और अलंकार: अनुप्रास (वर्ण आवृत्ति), उपमा (समानता), रूपक (अभेद आरोप); श्रृंगार रस का विषय नायक-नायिका।
Radio Communication and Electronics Fundamentals (RO/RM trade)
Ohm's law: V = IR; power P = VI = I²R = V²/R; series resistance adds, parallel 1/R = 1/R₁ + 1/R₂.
Frequency and wavelength: λ = c/f; 300 MHz gives 1 m, 30 MHz gives 10 m, 3 MHz gives 100 m (using c ≈ 3 × 10⁸ m/s).
Modulation: AM varies amplitude, FM varies frequency; FM has better noise immunity, AM has longer range at low bands.
Antenna basics: half-wave dipole length ≈ 143/f (MHz) metres; VSWR near 1:1 means good match; high VSWR reflects power back.
Propagation: HF (3–30 MHz) uses skywave via ionosphere, VHF/UHF are mostly line-of-sight; ground wave follows earth's curve at LF/MF.
Bandwidth and sidebands: AM signal bandwidth = 2 × modulating frequency; SSB carries one sideband and saves power.
Radio procedure: use plain language, phonetic alphabet (Alpha, Bravo, Charlie), prowords like ROGER (received), OVER (reply expected), OUT (end, no reply).
Emergency and distress: MAYDAY is distress (grave danger), PAN-PAN is urgency; call sign identifies station, procedure words keep transmissions short.
Semiconductors: diode conducts one way (forward bias), transistor amplifies in active region; rectifier converts AC to DC, filter capacitor smooths ripple.
Computer Fundamentals and Networking Basics
Memory units: 1 byte = 8 bits; 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.
Hardware: CPU = ALU + control unit + registers; RAM is volatile, ROM is non-volatile; cache is fastest, then RAM, then disk.
OS functions: process, memory, file and device management; GUI vs CLI; common OS examples Windows, Linux, macOS.
IP addressing: IPv4 is 32-bit (four octets 0–255), IPv6 is 128-bit; private ranges 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
Subnet mask defines network and host bits; /24 means 255.255.255.0 with 254 usable hosts.
OSI seven layers: Physical, Data Link, Network, Transport, Session, Presentation, Application; TCP works at Transport, IP at Network.
Protocols and ports: HTTP 80, HTTPS 443, FTP 21, SSH 22, SMTP 25, DNS 53, Telnet 23.
Topologies: star uses a central switch (easy fault isolation), bus shares one cable, ring passes token; LAN is local, WAN is wide area.
Security basics: firewall filters traffic, antivirus detects malware, strong password + encryption protect data; phishing is a social-engineering attack.