not clear on how to calculate the wait time

[learning_bee]

I am reading on TOm Kyte performance tuning workshop and I am not on this on top 5 events on statspack report:

events                       wait         time          %Total elapsed

Direct path write            5168         279           20.5

and he mentioned that there was 120 waits for direct path writes, totalling three thousandth second (as opposed to 279 seconds)

the question is how does he get 120 waits and 3,000 second???