Consider the above figure. Suppose the average object size is $1$Mbits and the average request rate from the institution$$s browsers to the origin servers is $10$ requests$/$sec$.$ The average time from when the Internet router forwards an HTTP request until the response is received is $3$ seconds. A traffic intensity of less than $\mathrm{.}8$ introduces a delay of tens of milliseconds. The link between the institutional router and the Internet router is $15$Mbps$.$

The average response time is the sum of the average access delay $($the delay from the Internet router to the institution router$)$ and the average Internet delay.

$1.$ Find the total average response time.

I got $3\mathrm{.}2$ seconds by using Total Avg Response Time $=$ Avg Access Delay $+$ Average Internet Delay

Answer:

$2.$ Now suppose a cache is installed in the institutional LAN. Suppose the miss rate is $0\mathrm{.}4.$ Find the total response time.

Answer: