Question

Senny and Farouk both drive delivery trucks. They leave the warehouse at the same time, but their routes are in opposite directions. Senny's rate is 10 mph more than Farouk's rate. After 6.5 hours, they are 520 miles apart. What are the rates of the trucks?

Answer 1

Senny: 45 mph; Farouk: 35 mph

Explanation:

Their combined speed is 520 mi/(6.5 h) = 80 mi/h. Senny's speed is half the sum of this and the difference of 10 mi/h:

... (80 mi/h + 10 mi/h)/2 = 45 mi/h

Farouk's speed is 10 mi/h less:

... 45 mi/h - 10 mi/h = 35 mi/h

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Comment on Sum and Difference Problems

If two numbers a and b have a sum of s and a difference of d, you can write equations ...

• a+b = s
• a-b = d

Adding these two equations gives ...

... 2a = s + d

Dividing this by 2 gives

... a = (s + d)/2 . . . . . . the formula we used above