Can you please explain College Board Test 5 Section 4 #37 and 38? They all use one table.


For #37, all you need to know is that average speed is calculated by dividing total distance by total time. The total distance is 0.6 + 15.4 + 1.4 = 17.4 miles.

We’re given a time of 24 minutes, but the question wants average speed in miles per hour, so convert 24 minutes to hours: 24\text{minutes}\times\dfrac{1\text{ hour}}{60\text{ minutes}}=0.4\text{ hours}

Average speed in miles per hour: \dfrac{17.4\text{ miles}}{0.4\text{ hours}}=43.5\text{ miles per hour}

For #38, note that the time she spends driving that’s not on the freeway is not impacted by her departure time, so all we care about for this question is that she can do 50 mph on the freeway for 15.4 miles if she leaves at 6:30 a.m., but it takes her 33% longer if she leaves at 7 a.m.

So how long is the 6:30 a.m. drive?

\dfrac{15.4\text{ miles}}{50\;\frac{\text{miles}}{\text{hour}}}=0.308\text{ hours}

What’s that in minutes?

0.308\text{ hours}\times\dfrac{60\text{ minutes}}{1\text{ hour}}=18.48\text{ minutes}

If she leaves at 7 a.m., that drive is 33% longer. The question is asking us how much time is added to her trip when she leaves at 7 a.m., so really it’s just asking us how many minutes that extra 33% amounts to. So, what’s 33% of 18.48 minutes?

18.48\text{ minutes}\times 0.33 = 6.0984\text{ minutes}

The question says round to the nearest minute, so our answer is 6.

Leave a Reply