Friday, November 2, 2012

TEXTBOOK: Pg. 61, Question # 21

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 5 km/h greater than Andrew's average speed. How much less time did Brian take, to the nearest minute.

SOLUTION:

Andrew: 234 km in 3 hours    Average Speed = ?

FORMULA:   Speed = Distance
Time

78 = 234
3

Speed = 78 km/ h

Brian: Has Average Speed of 5 km/ h greater than Andrew's.

78 + 5 = 83
Brian's Average Speed is 83 km/ h

To find out how much LESS time Brian took, we need to find out how much time Brian took FIRST!

To find how much time Brian took, you have to use the FORMULA: Distance divided by Speed to get the TIME.

D = T
S

234 km  ≈ 2.819
83 km/ h

Time  2.819 hours

2.819 hours x 60  169 minutes

169 minutes = 2 hours 49 minutes
(2 hours = 120 minutes, add remaining 49 minutes)

Time = 2 hours and 24 minutes

Now we subtract Brian's and Andrew's times to find out how much less time Brian took.

Andrew's Time - Brian's Time = Difference

3 hours 00 minutes - 2 hours 49 minutes = 11 minutes

SSA:  It took Brian 11 minutes less than Andrew to get from Dawson to Mayo in Yukon Territory.