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9 October 2015

Script for numerical ability of competitive exams

Important formulas of maths for competitive exams
  • n(n + 1)(2n + 1) is always divisible by 6.
  • 32n leaves remainder = 1 when divided by 8
  • n3 + (n + 1 )3 + (n + 2 )3 is always divisible by 9
  • 102n + 1 + 1 is always divisible by 11
  • n(n2– 1) is always divisible by 6
  • n2+ n is always even
  • 23n-1 is always divisible by 7
  • 152n-1 +1 is always divisible by 16
  • n3 + 2n is always divisible by 3
  • 34n – 4 3n is always divisible by 17
  • n! + 1 is not divisible by any number between 2 and n.(where n! = n (n – 1)(n – 2)(n – 3)…….3.2.1).
for example, 5! = 5.4.3.2.1 = 120 and similarly 10! = 10.9.8…….2.1= 3628800


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