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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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29 Statisticsandprobability

distributions

Contents 29.1 Introduction 933

29.2 Randomvariables 934

29.3 Probabilitydistributions--discretevariable 935

29.4 Probabilitydensityfunctions--continuousvariable 936

29.5 Meanvalue 938

29.6 Standarddeviation 941

29.7 Expectedvalueofarandomvariable 943

29.8 Standarddeviationofarandomvariable 946

29.9 Permutationsandcombinations 948

29.10 Thebinomialdistribution 953

29.11 ThePoissondistribution 957

29.12 Theuniformdistribution 961

29.13 Theexponentialdistribution 962

29.14 Thenormaldistribution 963

29.15 Reliabilityengineering 970

Reviewexercises29 977

29.1 INTRODUCTION

Engineersoftenneedtomeasuremanydifferentvariables,forexampletheoutputvoltage

of a system, the strength of a beam or the cost of a project. Variables are classified into

one of two types,discrete orcontinuous. These arediscussed inSection 29.2.

It is of interest to know the probability that a variable has of falling within a given

range. There is a high probability that a given variable will fall within some ranges,

and a small probability for other ranges of values. The way in which the probability is

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