explain about site bounce rate

hapter 3: Analytics Of 500 sessions that occurred on a website during a one-week period, 200 of them started on the homepage; 100 of these 200 sessions saw only the homepage before leaving the site. Of the 300 sessions that started on other pages, 100 of them consisted of only one pageview. What is the site bounce rate? 20% O 30% 40% 50%