Cumulative Assessment
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Think about the Distance Formula d=rt, where r is the rate of speed and t is the time.
80 second/feet
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=rt
d= 1000feet, t= 12.5seconds
.LHS /12.5seconds.=.RHS /12.5seconds.
Rearrange equation
a/b=.a /12.5./.b /12.5.
Note that as long as the ratio stays the same — 80 feet of distance for 1 second of time — we can express this rate in a couple different ways. Let's look at the choices we have been given.
| Fraction | Correct? | Why? |
|---|---|---|
| 80 second/feet | No | 80 second/feet=80 second/feet It takes the car 1 sec to travel 80 ft, not 80sec to drive 1 ft. |
| 80feet/second | Yes | This is exactly what we found when solving for rate. |
| 80 feet/second | Yes | 80feet/second=80 feet/second |
| second/80feet | Yes | The ratio is still correct even though it is flipped, as 1 second corresponds to a distance of 80 feet. |