Proving the memoryless property of the exponential distribution

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SUMMARY

The memoryless property of the exponential distribution states that for a random variable X with parameter β, the equation P(X ≤ a + b | X > a) = P(X ≤ b) holds true. The proof involves rewriting the left side as P((X ≤ a + b) ∧ (X > a)) / P(X > a) and utilizing the relationship P[(X ≤ a + b) ∧ (X > a)] = P[X ≤ a + b] - P[X ≤ a]. This leads to the conclusion that the exponential distribution's memoryless property is valid due to its disjoint ranges: a+b.

PREREQUISITES
  • Understanding of Exponential Distribution and its properties
  • Knowledge of conditional probability
  • Familiarity with probability notation and concepts
  • Basic skills in mathematical proof techniques
NEXT STEPS
  • Study the derivation of the exponential distribution's probability density function
  • Learn about other distributions with memoryless properties, such as the geometric distribution
  • Explore applications of the memoryless property in queuing theory
  • Investigate the implications of memoryless properties in stochastic processes
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Mathematicians, statisticians, and data scientists interested in probability theory and its applications, particularly those focusing on the exponential distribution and its unique properties.

DanielJackins
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Given that a random variable X follows an Exponential Distribution with parameter β, how would you prove the memoryless property?

That is, that P(X ≤ a + b|X > a) = P(X ≤ b)

The only step I can really think of doing is rewriting the left side as [P((X ≤ a + b) ^ (X > a))]/P(X > a). Where can I go from there?
 
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P[(X ≤ a + b) ^ (X > a)] = P[X ≤ a + b] - P[X ≤ a] , right?
 
Thanks. Using that I was able to prove it. But why is what you said true?
 
X has three disjoint ranges, <a, (a,a+b), >a+b.
P[(X ≤ a + b) ^ (X > a)] is the probability X is in the middle range.
P[(X ≤ a + b)] is the probability X is in the first or middle range.
P[X ≤ a] is the probability X is in the first range.
 

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