The time t required to drive a certain distance varies inversely with the speed r. If it takes 2 hours to drive the distance at 30 miles per hour, how long will it take to drive the same distance at 35 miles per hour?

Question

igreen · Answer

30 miles per hour for 2 hours is 60 miles.

60 / 35 = 1.71 hours

igreen · Answer

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vishweshshrimali5 · Answer

Okay see. This is a proportionality problem. Here:

$$\large{t \propto \cfrac{1}{r}}$$

$$\implies\large{t = \cfrac{k}{r}}$$

Now, from first part of the problem we have,

$$\large{2 = \cfrac{k}{30}}\tag{1}$$

If the required time is let t', then, 

$$\large{t' = \cfrac{k}{35}}\tag{2}$$

Now, from equations (1) and (2), you can obtain the correct answer.