The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 80%?  Pick one.
A) 6 B) 7 C) 9 D) 10 E) 11
We need on-time departure rate to be higher than 8/10, so it should be at least 9/11, which means that 9 out of 11 flights must depart on time. Since for now 3 out of 4 flights departed on time then  9-3= 
<gadget id="calculator"> 9-3</gadget>
<output>6</output>
6 subsequent flights need to depart on-time.   6nswer: 6
<result>A</result>
The first flight out of Phoenix airport had a late departure. If the next three flights departed on-time, how many subsequent flights need to depart from Phoenix on-time, for the airport's on-time departure rate to be higher than 80%?