What was his speed after sun up

Question

Jim drove his truck 5 hours before dawn and 6 hours after sun up. If his average speed was 5 mph more in the dark and he covered 630 total miles. What was his speed after sun up

Answer 1

Let's use the variable d for average mph in the dark, and s for average mph in the sun. We can set up the following system of equations:

 

5d + 6s = 630

d = s + 5

 

Substituting s + 5 for d in the first equation, we find:

 

5(s + 5) + 6s = 630

5s + 25 + 6s = 630

11s + 25 = 630

11s = 605

s = 55mph

 

Now plug in 55 for s in the second equation:

 

d = s + 5

d = 55 + 5

d = 60

 

Check:

 

5(60) + 6(55) =

300 + 330 = 630

 

So Jim's speed after sun up is 55mph.