Exercise 9 Page 49

The distance d the car traveled was 1000 feet and the time t it took was 12.5 seconds. We can find the rate of speed r using the Distance Formula. d=rtWe will substitute the values into the formula and then solve for r.

d=rt

SubstituteII

d= 1000feet, t= 12.5seconds

1000feet=r( 12.5seconds)

DivEqn

.LHS /12.5seconds.=.RHS /12.5seconds.

1000feet/12.5seconds=r

RearrangeEqn

Rearrange equation

r=1000feet/12.5seconds

ReduceFrac

a/b=.a /12.5./.b /12.5.

r=80feet/second

Note that as long as the ratio stays the same — which is 80 feet for 1 second — we can express this rate in a couple different ways. Let's look at the choices we have been given.

Fraction	Correct?	Why?
80second/feet	No	80 secondfeet= 80secondfeet It takes the car 1 s to travel 80 ft, not 80s to drive 1 ft.
80feet/second	Yes	This is exactly what we found when solving for rate.
80feet/second	Yes	80feetsecond=80 feetsecond
second/80feet	Yes	Even though it is flipped the ratio is still correct, as 1 second corresponds to a distance of 80 feet.