smc

Question

Mr. Earl E. Bird gets up every day at 8:00 AM to go to work. If he drives at an average speed of 40 miles per hour, he will be late by 3 minutes. If he drives at an average speed of 60 miles per hour, he will be early by 3 minutes. How many miles per hour does Mr. Bird need to drive to get to work exactly on time?

Accepted Answer

Let the time he needs to get there in be t and the distance he travels be d. From the given equations, we know that d=(t+120)40 and d=(t-120)60. Setting the two equal, we have 40t+2=60t-3 and we find t=14 of an hour. Substituting t back in, we find d=12. From d=rt, we find that r, our answer, is 48.