Question

Kirk’s average driving speed is 5 kilometers per hour faster than Thor’s. In the same length of time it takes Kirk to drive 525 kilometers, Thor drives only 490 kilometers. What is Kirk’s average speed?

Answer 1

Let K and T be the speeds of Kirk and Thor respectively.

Note the standard definition that d=vt, distance equals velocity times time.

t=d/v

For Kirk, t=525/(T+5)

For Thor, t=490/T

Since we are told that they have traveled the same amount of time we can say t=t which leaves us:

525/(T+5)=490/T  multiply both sides by T

525T/(T+5)=490  multiply both sides by T+5

525T=490T+2450  subtract 490T from both sides

35T=2450  divide both sides by 35

T=70

So Thor's average speed is 70kph, since K=T+5

K=75kph

So Kirk's average speed is 75kph