Harvey's Scribepost for November 4, 2011

2.2 Apply, Question 21, page 61

Andrew drove his car 234 km from Dawson to Mayo in Yukon Territory in 3 h. Brian drove his truck along the same route at an average speed of 5km/h greater than Andrew's average speed. How much less time did Brian take, to the nearest minute?

If we divide 234km by 3h, we should get the km. We need to get Andrew's average speed because we need it to find out how long Brian took to reach the same distance.

78=234/3

So Andrew drove his truck at 78km/h.

We know that Brian drove 5km/h faster than Andrew, so he would have driven at 83km/h.

To find out how long he drove, we divide 234km by 83km.
2.819277108=234/83

Round.
2.8=234/3

Brian drove at 83km and took 2.8 hours.

We need to know how much more faster Brian was compared to Andrew. To do that, we convert the hours into minutes. To do this, multiply the hours by 60 minutes.

Andrew:
180=60*3

Brian:
168=60*2.8

Then subtract, and we have our answer.
12=180-168

Brian was 12 minutes faster than Andrew to reach the same distance.