Question

The time t required to drive certain distance varies inversely with the speed r. It takes 2 hours to drive the distance at 40 miles per hour,how long will it take to drive the same distance at 45 miles per hour?

Answer 1

Answer:

$\frac{16}{9}$  hours

Step-by-step explanation:

Whenever 2 quantities (suppose a and b) are inversely proportional to each other, we can write an proportionality equation (with k as proportional constant) as:

$a=\frac{k}{b}$

Since, here t is INVERSELY PROPORTIONAL to r, we can say:

$t=\frac{k}{r}$

Firstly, we have t = 2 hour and r = 40 mph, so we find k:

$t=\frac{k}{r}\\2=\frac{k}{40}\\k=2*40\\k=80$

Now, secondly, we have r = 45 and k = 80, we need to find t:

$t=\frac{80}{45}\\t=\frac{16}{9}$

So, it would take  $\frac{16}{9}$  hours