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 60%?
I will see what is the quickest way to solve it then I will provide the explanation	Choose the correct choice from the following choices: A) 6 B) 7 C) 9 D) 4 E) 11
The following approach might be the easiest one and less error prone.   We need on-time departure rate to be higher than 6/10, so it should be at least 7/11, which means that 7 out of 11 flights must depart on time. Since for now 3 out of 4 flights departed on time then  7-3= 
<gadget id="calculator"> 7-3</gadget>
<output>4</output>
4 subsequent flights need to depart on-time.   Answer: 4
<result>D</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 60%?
I will see what is the quickest way to solve it then I will provide the explanation