Bunuel
Laura and Jeff plan to drive along the same route to the same destination. If it will take one hour for Jeff to travel the route, and Laura travels at a rate that is 50% faster than Jeff's rate, how long will it take Laura?
A. 30 minutes
B. 35 minutes
C. 40 minutes
D. 45 minutes
E. 50 minutes
Assign a valueJeff and Laura travel the same distance, D
We have
• a time for Jeff
• a rate for Laura in relation to Jeff
Given any distance, D, variable or assigned, we can
• find Jeff's rate and thus Laura's rate, and
• find Laura's time
Let
D = 4 miles
• Jeff's rate? Jeff drives D = 4 miles in t = 1 hour
J's
rate:
\(\frac{D}{t}=\frac{4}{1}\)= 4 mph
• L's
rate, 50% faster than J's =
\((1.5 * 4)=6\) mph
• L's
time?
\(T=\frac{D}{r}=\frac{4}{6}=\frac{2}{3}\) hour
L's time = 40 minutes
ANY fraction of an hour * 60 = minutes. So
\(\frac{2}{3}*60=40\)mins)
Answer CAlgebra (or inverse proportion)Let Jeff's rate =
\(J\)Let Laura's time =
\(t_2\)Jeff's time in minutes: 1 hour =
\(60\)(Answers are in minutes)
• Overall strategy: Use equal distance to find Laura's time
1) Find distance in terms of Jeff, D = r*t
Jeff drives at rate
\(J\) mph for 60 minutes
D in terms of Jeff =
\((r*t)=(J*60)= 60J\)2) Find distance in terms of Laura, D = r*t
Laura's rate? She drives 50% faster than Jeff
L's
rate:
\((J+\frac{1}{2}J)=\frac{3}{2}J\)L's
time =
\(t_2\)D in terms of Laura =
\((r*t)=(\frac{3}{2}J*t_2)\) 3)
D = D. Set distances equal, solve for Laura's time
\(\frac{3}{2}J * t_2 = 60J\)
So \(t_2 =\frac{60J}{(\frac{3}{2})J}=(60J*\frac{2}{3}J)=40\) minutes
Laura's time, \(t_2 = 40\) minutes
Answer C*
Note: rate and time are inversely proportional. Distances are equal.
Flip Laura's rate, \(\frac{3}{2}J\),
to get Laura's time, namely, \(\frac{2}{3}J\).
If J's time is in hours, convert L's final time to minutes. Much quicker, though perhaps not as easy to see.