Question 949795
r=rate of plane in still air
300 miles/r-20mph=400 miles/r+20 mph Multiply each side by(r-20mph)
300 miles= 400 mi(r-20 mph)/r+20 mph Multiply each side by (r+20 mph)
300 miles(r+20 mph)=400 miles(r-20 mph)
300r+6000mph=400r-8000mph Add 8000mph to each side.
300r+14000mph=400r Subtract 300r from each side.
14000mph=100r Divide each side by 100.
140 mph=r ANSWER: The rate of the plane in still air would be 140 mph
CHECK:
300 mi/140mph-20mph=400 mi/140mph+20mph
300mi/120mph=400mi/160mph
2.5 hrs=2.5 hrs