6. 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 40 miles per hour, how long will it take to drive the same distance at 45 miles per hour?

A. 80 hours

B. 900 hours

C. about 1.78 hours

D. 2.25 hours

C. about 1.78 hours

Step-by-step explanation:

1.78 hours

Step-by-step explanation:

If t varies inversely with the speed, the formula for that is  t= \frac{k}{r} .  If t = 2 and r = 40, then we can solve for k, the constant of variation.  Multiply both sides by 40 to get  k = 80.  Now we need to find the value for t when r = 45.  Using the k value we just solved for, we will fill in the equation as  t= \frac{80}{45}   for a t value of about 1.78 hours

about 1.78 hours

t = k/r

2 = k/67

k = 134 (which happens to be the distance)

t = 134/r

t = 134/55

t = 2.436 hours

The formula for this is t = k/r, read "t varies inversely as r". If the info they give us is 4 hours and 35 miles per hour, we find that k = 140. Now use that 140 in another equation to solve for t: t = 140/45, and t = 3.1 hours

t = k/r\

4 hours and 35 miles per hour,

we find that k = 140.

Now use that 140 in another equation to solve for t:

t = 140/45, and

t = 3.1 hours