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Probability

  • Complementary Probability: P(A’)=1−P(A)
  • Shortcut for "At least one" problems: P(At least one)= 1− P(None)
  • "At Most":
    P(X≤N)= P(X=1)+P(X=2)+P(X=3) + … + P(X=N)

Divisibility

Primes of number n: [where n=p1^e1 * p2^e2 * … * pn^en]
then Number of divisors = (e1+1) * (e2+1) * … * (en+1)

Example: 60=2^2 × 3^1 × 5^1 -> then 60 has (3 x 2 x 2) = 12 divisors

Interest

  • Simple Interest (SI): (P x R x T) / 100 [if % is taken as x/100 ex: 10% = 10/100] or else: (P x R x T) [if % is taken as decimal ex: 10% = 0.10]

    • P = Principal amount
    • R = Rate of interest per annum
    • T= Time in years

Amount at End: P + Simple Interest = P * (1 + (RT)/100 )

Compound Interest: [ P x (1 + R)^T ] - P

Percentage

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