<p>A car traveled 10 miles at an average speed of 20 miles per hour and then traveled the next 10 miles at an average speed of 40 miles per hour. What was the average speed, in miles per hour, of the car for the 20 miles?</p>
<p>The answer is 80/3. </p>
<p>Can anyone explain the question?</p>
<p>There is a way to manipulate d=rt formula, but I don’t know how. Use this cheater formula.
average speed = 2(speed 1 X speed 2) / (speed 1 + speed 2)
this yields 2(20)(40)/(20+40) = 80/3</p>
<p>***** only works in mph</p>
<p>Any standard way of solving this? Anyone?</p>
<p>Trip took a total of 3/4 hours (10 miles / 20mph + 10 miles/40 mph) with 1/4 hours of the trip being driven at 40 mph and 1/2 hours of the trip being driven at 20 mph.</p>
<p>d = rt
20 miles = r * .75 hours
r = 20/.75mph or 26.6666… mph</p>
<p>The key is finding how long the trip took.</p>
<p>A car traveled 10 miles at an average speed of 20 miles per hour and then traveled the next 10 miles at an average speed of 40 miles per hour. What was the average speed, in miles per hour, of the car for the 20 miles?</p>
<p>DISTANCE = AVERAGE VELOCITY * TIME</p>
<p>For the first 10 miles…</p>
<p>d = vt
10 = 20t
t = 0.5 hrs</p>
<p>Then for the next 10 miles…</p>
<p>10 = 40t
t = 0.25hrs</p>
<p>Solve d=vt for v.</p>
<p>d = v * t
v = d/t</p>
<p>Now, you know that…</p>
<p>d = 10 + 10
t = 0.5 + 0.25</p>
<p>So…</p>
<p>v = 20 / 0.75</p>
<p>Which is equal to 80/3.</p>
<p>A car traveled 10 miles at an average speed of 20 miles per hour and then traveled the next 10 miles at an average speed of 40 miles per hour. What was the average speed, in miles per hour, of the car for the 20 miles?</p>
<p>Easiest way to solve it:
How many miles did the car travel in total? 20 miles (10 + 10)
How many minutes did the trip take? 45 minutes (10 miles at 20mph would be 30 minutes, and 10 miles at 40mph would be 15 minutes. 30 + 15 = 45)
20/45, just get this with a 60 in the denominator; all you do is multiply 20 by 1.33333333 and then you get the answer: 26.66 repeating or 80/3</p>
<p>Thanks I understood the explanation</p>