SOLUTION: What is the speed of a car if an increase of 5km/h saves 24 minutes in covering 180km?

Question 806553: What is the speed of a car if an increase of 5km/h saves 24 minutes in covering 180km?
Answer by thejackal(72) (Show Source): You can put this solution on YOUR website!
D = 180 Km, S = S Km/h, T = T hours
D = S x T therefore 180 = S x T
but with an increase of 5 km/h the same distance can be done in 24/60 hours less
therefore 180 = (S + 5) x (T - 0.4)
now we have a simultaneous equation
express T as a function of S thus T in the first equation = 180/S
plug this new function of T in the second equation like so
180 = (S + 5) x ((180/S) - 0.4)
solve for S and you will find that S, the original Speed is = 45Km/h
Now that you know S, plug it into the function for Time T such that T = 180/S = 180/45 = 4 hours. The reason you want to calculate the original time T is so that you can confirm your answer for S like so
180 = (45 + 5) x (4 - 0.4) if this is true (which it is) then your done
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