Question

You send out 12,000 emails and 300 are opened. What is your open rate? (Open rate is opens as a percentage of sent emails.)

Answer 1

Amount of emails which are sent = 12,000
Amount of emails which are opened = 300

the question asked the open rate as a percentage. 

Hence, we can write open rate as,
        Open rate = (number of opened emails / number of sent emails) x 100%
                          = (300 / 12,000) x 100%
                          = 2.5 %