RRB NTPC — Important Topics & Questions
Mathematics
Q: Number system — find HCF and LCM of 36, 48, 60.
Prime factorisation:
36 = 2² × 3²
48 = 2⁴ × 3
60 = 2² × 3 × 5
HCF = product of LOWEST powers of common primes
= 2² × 3 = 4 × 3 = 12
LCM = product of HIGHEST powers of all primes
= 2⁴ × 3² × 5 = 16 × 9 × 5 = 720
Quick check: HCF × LCM = product of numbers (only for TWO numbers)
12 × 720 ≠ 36×48×60 (rule is for two numbers only, not three)
Q: Average age of 5 people is 30. If one aged 40 is replaced by someone aged 20, new average?
Old sum of ages = 5 × 30 = 150
New sum = 150 - 40 + 20 = 130
New average = 130/5 = 26
Shortcut: Change in total = -40 + 20 = -20
Change in average = -20/5 = -4
New average = 30 - 4 = 26
General Intelligence
Q: Coding-decoding — if PENCIL is coded as RGPEKN, decode MARBLE.
P → R (P+2) | E → G (E+2) | N → P (N+2) | C → E (C+2) | I → K (I+2) | L → N (L+2)
Pattern: each letter shifted +2 in alphabet
MARBLE: M+2=O | A+2=C | R+2=T | B+2=D | L+2=N | E+2=G
MARBLE → OCDTNG
General Awareness
Q: What is the gauge used in Indian Railways? What are different gauges?
GAUGE = distance between the two rails
Indian Railways gauges:
Broad Gauge (BG): 1676 mm (5 ft 6 in) — STANDARD in India, 90% of network
Metre Gauge (MG): 1000 mm (1 metre) — being converted to BG (Project Unigauge)
Narrow Gauge (NG): 762 mm or 610 mm — hill railways, Darjeeling, Kalka-Shimla
World standard gauge (used in Europe): 1435 mm
India uses broader gauge for stability in subcontinent conditions
Fastest train: Vande Bharat Express (160 km/h design speed)
Longest platform: Hubballi (1,505 m)
First railway in India: Bombay (VT) to Thane, 1853 (34 km)
Q: Scientific names of common animals — railway GA questions.
Humans: Homo sapiens
Tiger: Panthera tigris (national animal of India)
Lion: Panthera leo
Elephant: Elephas maximus (Asian)
Peacock: Pavo cristatus (national bird)
Lotus: Nelumbo nucifera (national flower)
Mango: Mangifera indica (national fruit)
Gangetic Dolphin: Platanista gangetica (national aquatic animal)
Cow: Bos taurus/indicus
Buffalo: Bubalus bubalis
Revision Notes
RRB NTPC PATTERN:
CBT 1: 100Q, 90 min, 0.33 negative | CBT 2: 120Q, 90 min, 0.33 negative
Sections: Mathematics + General Intelligence + General Awareness
MATHEMATICS FOCUS:
Number system: HCF/LCM, prime factorisation, divisibility
Arithmetic: percentage, ratio, average, SI/CI, profit-loss
Time-work-speed, pipes, mixtures
Mensuration: areas, volumes of standard shapes
Elementary statistics: mean, median, mode
RAILWAY GK (high value):
First/fastest/longest/highest in Indian Railways
Railway zones and headquarters
Railway Budget (now merged with Union Budget 2017)
Major railway projects: DFC, high-speed rail, metro projects
Railway safety features: Kavach, LHB coaches
