# Distance problem

• Feb 12th 2013, 10:02 AM
dannyc
Distance problem
Carmen drove from Blairtown to Ore City, a distance of 80 miles. From Ore City she drove to Janesville, and the drove back to Blairtown. The ratio of Carmen's driving times on the first, second, and third segments of the trip, respectively, was 5:2:4, and she drove at the same average speed on each segment. What was Carmen's total driving distance, in miles, for the 3 segments of the trip?

I know it is 176, but how do I show it algebraically?
• Feb 12th 2013, 10:18 AM
emakarov
Re: Distance problem
Hint: Since the average speed is the same, the ratio of distances is the same as the ratio of times. Indeed, let's say it took $\displaystyle t_1$ hours to drive from Blairtown to Ore City and $\displaystyle t_2$ hours to drive from Ore City to Janesville, and let the average speed be $\displaystyle v$. Then the distance between Blairtown and Ore City is $\displaystyle vt_1$ and the distance between Ore City and Janesville is $\displaystyle vt_2$. The ratio of these distances is $\displaystyle \frac{vt_1}{vt_2}=\frac{t_1}{t_2}=\frac{5}{2}$ is the same as the ratio of times.
• Feb 12th 2013, 10:19 AM
dannyc
Re: Distance problem
Right, but how do i show it with 3 ratios?
• Feb 12th 2013, 10:19 AM
jakncoke
Re: Distance problem
$\displaystyle \frac{5}{80} = \frac{2}{x}$, x = 32 is the distance from Ore city to janesville.

$\displaystyle \frac{5}{80} = \frac{4}{x}$, x = 64 is the distance from janesville to blairtown.

so 64+32+80 = 176 is total driving distance
• Feb 12th 2013, 10:28 AM
emakarov
Re: Distance problem
Quote:

Originally Posted by jakncoke
$\displaystyle \frac{5}{80} = \frac{x}{2}$, x = 32 is the distance from Ore city to janesville.

Hmm, there is something wrong about this proportion. I would say, 80 : x = 5 : 2 where x is the distance from Ore City and Janesville.
• Feb 12th 2013, 10:32 AM
jakncoke
Re: Distance problem
Quote:

Originally Posted by emakarov
Hmm, there is something wrong about this proportion. I would say, 80 : x = 5 : 2 where x is the distance from Ore City and Janesville.

yes, i miswrote, i corrected it.