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carollaw
10-06-2008, 07:41 PM
I'l having aproblem with distance. I know that d=rt but I cant seem ot solve the following:

Carol and Marla drove a total of 258 miles in 5 hours. Carol drove the first part and averaged 53 mph. Marla drove the rest and averaged 51 mph. For approx how many hours did Marla drive?

Subhotosh Khan
10-06-2008, 09:21 PM
I'l having aproblem with distance. I know that d=rt but I cant seem ot solve the following:

Carol and Marla drove a total of 258 miles in 5 hours. Carol drove the first part and averaged 53 mph. Marla drove the rest and averaged 51 mph. For approx how many hours did Marla drive?

Name things first:

Miles(d) driven by Carol = C

Miles driven by Marla = M

Total miles driven = C + M = 258............................................... .......(1)

Time (d/r) driven by Carol = C/53

Time (d/r) driven by Marla = M/51

Total time driven = 5 = C/53 + M/51................................................ .(2)

You have two equations - two unknowns - solve it.

soroban
10-07-2008, 03:06 PM
Hello, carollaw!

Carol and Marla drove a total of 258 miles in 5 hours.
Carol drove the first part and averaged 53 mph.
Marla drove the rest and averaged 51 mph.
For how many hours did Marla drive?
\text{Let }x\text{ = hours that Marla drove.}

. . \text{At 51 mph, she drove: }\:51x\text{ miles.}

\text{Carol drove the other }5-x\text{ hours.}

. . \text{At 53 mph, she drove: }\:53(5-x)\text{ miles.}

\text{Together, they drove a total of: }\:51x + 53(5-x)\text{ miles.}

\text{But we are told they drove a total of 258 miles.}