Chris and his brother leave the same point and run in opposite directions on a straight road. after running for 3 hours they are 18 miles apart. if chris runs an average of 1 mph fast than his brother what is chris's average speed

Chris' average speed is 3.5mph: Lets take Chris' brother speed = B then Chris speed = (B+ 1) mphgiven in the question and: The average speed for covering 18 miles= chris' average speed + his brother's average speed = (B+ 1) + B since Speed = Distance covered / time taken then average speed for 18 miles can also be found by: 18 miles/3 hours = 6 miles per hour then we have; (B+ 1) + B = 6mph (B +1) = (6-B) B+B = 6-1=5 2B=5 B=5/2=2.5 mph (this is Chris' brother average speed) Hence Chris' average speed is = B+1= 2.5+1= 3.5mph