Joe is trying to soup up his dragster. he knows that the time needed for the car to go from 0 to 100 miles per hour varies inversely with the car's horsepower. at 200 horsepower, the car can go from 0 to 100 mph in 10 seconds. how long should the car take if he can increase the horsepower to 250 hp?

8 seconds

The hardest part of this is setting up the equation -- the calculations are pretty easy.

You're told that the time (needed to go from 0 to 100 MPH) is inversely proportional to the horsepower:  what this means is that as horsepower gets larger, time gets smaller. This makes sense since the more horsepower you have, the less time it will take you to get to 100 MPH

You can think of this as:

200 HP = 10 seconds
250 HP = x seconds

You set the equation up as:

250 HP / 200 HP = 10 sec / x sec

Now, just cross multiply and solve:

250 / 200 = 10 / x
250x = (200 x 10)
250x = 2000
x = 2000 / 250
x = 8

So, as you increase the horsepower from 200 to 250, the time decreases from 10 seconds to 8 seconds.

Hope this helps!

Good luck.