Example 1: There are two tasks. Task 1 duration follows a normal distribution with mean 5 days and standard deviation of 1 day. Task 2 duration follows an uniform distribution between 3 and 7 days. What is the probability both tasks get completed in 10 days if sequentially done? Same question if done in parallel. What is the median time completion in both cases? Solution: - Simulate times:

T1 = rnorm(1000,5,1)
T2 = runif(1000,min=3,max=7)
  • Compute probability for sequential project

    S = T1 + T2 sum(S<10)/1000

  • Compute probability for parallel project

    P = pmax(T1,T2) sum(P<10)/1000

  • Compute medians:

    median(S) median(P)

pmax function example: > x <- c(3, 26, 122, 6) > y <- c(43,2,54,8) > z <- c(9,32,1,9) > pmax(x,y,z) [1] 43 32 122 9


Example 2: Phoncessories manufactures several customized accessories for smart phones and packages them into boxes. Each box consists of 20 units. Processing each unit in a box takes 2 minutes (constant). Company classifies the boxes into “simple” (ordered 60% of the time) and “complex” (ordered 40% of the time): Simple box setup time is exponential dist. with mean = 1 hour Complex box setup time is exponential dist. With mean = 1.5 hours The firm would like to study the overall time to process a random order for a box.

This is the code to generate a sample of production times for 1,000 boxes: TSimple=rexp(1000,rate=1/60) TComplex=rexp(1000,rate=1/90) OrderType=sample(c(0,1),size=1000,replace=TRUE,prob=c(0.6,0.4)) ProdTime=ifelse(OrderType==0,TSimple,TComplex)+40