Understanding Divisibility Rules | UPSC CSAT Quantitative Aptitude Made Easy | PGP

In this class, we crack the Divisibility Rules that power fast elimination and accurate calculation in UPSC CSAT Paper-II and other aptitude exams. Starting from powers of 2 and 5, moving to 3, 9, 11, and ending with smart tests for 6, 12, 15, 24, 36, 14, 40, 7 and 13, you’ll learn the logic behind each rule—not just shortcuts—so you can apply them to any number with confidence.

What you’ll learn :

✅ Powers of 2: last-digit logic → 2, 4, 8, 16, 32 (check last 1/2/3/4/5 digits)
✅ Powers of 5: last-digit logic → 5, 25, 125 (check last 1/2/3 digits: 00/25/50/75)
✅ Sum-of-digits tests → 3 and 9 (plus the grouping trick to avoid addition errors)
✅ 10: numbers ending with 0
✅ 11: difference of sums of alternate positions
✅ Composites via co-prime factorization:

6 = 2×3, 12 = 3×4, 15 = 3×5, 24 = 3×8, 36 = 9×4, 14 = 2×7, 40 = 8×5

If divisible by both co-prime factors ⇒ divisible by their product

✅ Practical tests for 7 & 13 using 3-digit grouping (difference method)
✅ PYQ-style examples: numbers like XYZXYZ, 7x + 96, and 99 nines ÷ 13

Who is this for?
UPSC Prelims CSAT (Paper-II) aspirants
KPSC & other State PSC exams
SSC, Banking, Insurance & aptitude tests

Boost your prep
Improve speed, accuracy, and elimination
Build rock-solid Number System fundamentals
Solve PYQ-style questions confidently

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🔔 Next up in Number System: LCM & HCF
📍 Simplifying CSAT Preparation with Conceptual Clarity & Smart Tricks.

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