Assume that we have 100 pages of physical memory.

Let's start at time t = 0. You want to serve the request:

+ 2 100       --> starting a process and allocating memory is very
                  fast in our simulation, this happens instantnously: 
                  T doesn't change (== 0)

w 2 42        --> writing page 42 takes T_mem_access. T += T_mem_access

+ 3 70        --> here we want to start process 3, which needs 70 pages
                  of memory. This requires swapping process 2 out, meaning
                  you've to write 100 pages to disk: 
                       T += 100 * T_disk_write


w 3 21        --> reading page 21: T += T_mem_access
r 2 42        --> swapping out process 3: T += T_disk_write * 70
                  swapping in process 2:  T += T_disk_read * 100
                  reading page 42: T += T_mem_access


---> total time = T 
---> number of accesses: 3 (two write, one read)
---> average memory utilization:
     % memory used on average: 100 % (+ 2 100)
                                70 % (+ 3 70)
                               100 % (+ 2 42)
                              -----
                                90 %