word problems, algebra ?
Raul flew his plane 200 mi against the wind in the same time it took him to fly 400 mi with the wind. If the speed pf the wind was 50 mi per hour, what was the average speed of his plane?
If y varies inversly as x, and y=27 when x=4, find y when x=12
The force required to compress a spring varies directly as the change in the length of the spring. If a force of 12 pounds is required to compress a spring 3 inches, how much force is required to compress the spring 5in?
My answers were 100 mi, 81, and 20 and all wrong 
Comments
1) Let his speed in still air be x mph
200/ (x -50) = 400 / ( x+50)
CROSS MULTIPLY
400x - 20000 = 200x + 10000
200x = 30000
x = 150 mph
200 / 100 = 2 hours
400 / 200 = 2 hours
600 /4 = 150 mph ANSWER