Answer:
5
Step-by-step explanation:

Answer:
2 should be the correct one.
Answer:
1/2, 9/16, 5/8, 3/4
Step-by-step explanation:
let the speed of plane in still air be x and that wind be y
therefore:
x+y=490
x-y=390
next we solve for the values of x and y, first we add the above equations. This will give us:
2x=880
x=880/2
x=440 miles per hour.
substituting the value of x in one of the equations and solving for y we get:
440+y=490
y=490-440
y=50 miles per hour