Probability practice

Geometric Distribution worksheets

Model the number of trials through the first success using exact, cumulative, tail, mean, and variance questions.

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Let X count trials through the first success, so X has support 1, 2, .... Assume independent trials with constant success probability and round only final probabilities.

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Each worksheet states the sample-space assumptions, distribution support, and counting convention needed for the selected model. Probability tables stay fully labeled, and Bayes questions identify the conditioning event before reversing it.

Learning objective

What this activity builds

Use the trials-through-first-success convention consistently for geometric probabilities and moments.

Worked example

With p=1/4, find the probability that the first success occurs on trial 3.

(3/4)^2(1/4)=9/64.

Trials 1 and 2 must fail, and trial 3 must succeed.

Teaching notes

Make the practice count

  • Write the counting convention beside X.
  • For X>=k, require k-1 initial failures.
  • Distinguish first success by k from first success exactly at k.

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Math SheetNameScoreTeacherDateGeometric DistributionLet X count trials through the first success, so X has support 1, 2, .... Assume independent trials with constant success probability and round only final probabilities.1.Let X count trials through the first success, with p = 9/20. Find the mean and population variance of X.Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....2.Let X count trials through the first success, with p = 1/4. Find P(X >= 5), meaning at least 5 trials are required.Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....State assumptions and round only the final probability.math-sheet.comPage 1 of 4
Math SheetNameScoreTeacherDateGeometric DistributionLet X count trials through the first success, so X has support 1, 2, .... Assume independent trials with constant success probability and round only final probabilities.3.Let X count trials through the first success, with p = 11/20. Find P(X <= 7), the first success by trial 7.Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....4.Let X count trials through the first success, with p = 3/10. Find P(X = 3).Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....State assumptions and round only the final probability.math-sheet.comPage 2 of 4
Math SheetNameScoreTeacherDateGeometric DistributionLet X count trials through the first success, so X has support 1, 2, .... Assume independent trials with constant success probability and round only final probabilities.5.Let X count trials through the first success, with p = 1/20. Find P(X = 2).Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....6.Let X count trials through the first success, with p = 17/20. Find the mean and population variance of X.Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....State assumptions and round only the final probability.math-sheet.comPage 3 of 4
Math SheetNameScoreTeacherDateGeometric DistributionLet X count trials through the first success, so X has support 1, 2, .... Assume independent trials with constant success probability and round only final probabilities.7.Let X count trials through the first success, with p = 3/4. Find P(X >= 9), meaning at least 9 trials are required.Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....8.Let X count trials through the first success, with p = 2/5. Find P(X <= 6), the first success by trial 6.Assumptions: Trials are independent with constant success probability; X includes the successful trial and has support 1, 2, ....State assumptions and round only the final probability.math-sheet.comPage 4 of 4

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