How long does he drive at 45 mph

Question

A man drives for a while at 45 mph. Realizing that he is running late, he increases his speed to 60 mph and completes his 405-mile trip in 8 hours.

Answer 1

If he drives t hours at 45 mph

then he drives (8-t) hours at 60 mph

Total distance is 405 miles

 

Distance = rate*time ... d=rt

 

405 = 45t + 60(8-t)

 

45t + 480 - 60t = 405

-15t = 405 - 480

-15t = -75

t = -75/(-15)

t = 5 hours driving time at 45 mph