Question 115488

Distance(d) equals Rate(r) times Time(t) or d=rt; r=d/t and t=d/r



Let r=rate (speed) of the plane in still air
(Note: with the wind, add wind speed; against the wind, subtract wind speed)
time flying with the wind=465/(r+20)
time flying against the wind=345/(r-20)
And we are told that the above times are equal, so:

465/(r+20)=345/(r-20)  multiply each side by (r+20)(r-20){or cross-multiply}
465(r-20)=345(r+20) get rid of parens (distributive law)

465r-9300=345r+6900  subtract 345r from and add 9300 to both sides
465r-9300+9300-345r=345r-345r+6900+9300  collect like terms
120r=16200  divide both sides by 120
r=135mph--------------------------------speed of the plane in still air

CK
465/(135+20)=345/(135-20)
465/155=345/115
3=3

Hope this helps---ptaylor