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Word problems solved by substitution

Leslie and Gilbert drove a total of 447 miles in 11 hours. Leslie drove the first part of the trip and averaged 55 miles per hour. Gilbert drove the remainder of the trip and averaged 35 miles per hour. for what length of time did Leslie drive ?

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1 Answer

let L be time Leslie drove

let G be time Gilbert drove

L + G = 11

55L + 35G = 447

L = 11 - G

55 * (11 - G) + 35G = 447

605 - 55G + 35G = 447

605 - 20G = 447

-20G = 447 - 605

-20G = -158

G = 7.9 hours

therefore L = 11 - 7.9 = 3.1 hours.

so, G = 7.9 hours and L = 3.1 hours