Last digit of a random power equal to one
Question
Choose uniformly from and, independently, uniformly from the twenty integers . Find the probability that the last digit of is .
Short answer
. Only last digits matter. Powers of always end in (20 values of ); and end in when (5 values each); does when is even (10 values); never does. That is of the equally likely pairs.
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Open the worked solutionLessons behind this question
- Counting and Combinatorics
- Sample Spaces, Events, and the Probability Axioms
- Conditional Probability, Total Probability, and Bayes' Rule
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