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 40%?
I will see what is the quickest way to solve it then I will provide the explanation
Choose one
A) 6  B) 2  C) 9  D) 10  E) 11
The following approach might be the easiest one and less error prone.   We need on-time departure rate to be higher than 4/10, so it should be at least 5/11, which means that 5 out of 11 flights must depart on time. Since for now 3 out of 4 flights departed on time then  5-3= 
<gadget id="calculator"> 5-3</gadget>
<output>2</output>
2 subsequent flights need to depart on-time.   Answer: 2.
<result>B</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 40%?
I will see what is the quickest way to solve it then I will provide the explanation