Question

Marge drive 290 miles in five hours. Three hours were on the interstate, then the remainder of the trip was on a road that caused her to reduce her speed by 20 mph. How fast did Marge drive on the interstate?

Answer 1

Marge drove by 66 miles per hour on the interstate

Step-by-step explanation:

Marge drive 290 miles in five hours, her trip has two stages

1. She drove 3 hours on the interstate
2. The remainder of the trip was on a road that caused her to reduce her speed by 20 mph

We need to find how fast Marge drove on the interstate

Assume that she drove by speed x miles per hour on interstate

∵ Distance = speed × time

∵ Her speed on the interstate is x mph

∵ The time of interstate is 3 hours

∴ The distance of interstate = x × 3 = 3x miles

∵ The time of the total trip is 5 hours

∵ She spent 3 hours on the interstate

∴ The time of the remainder of the trip = 5 - 3 = 2 hours

∵ She reduced her speed 20 mph for the remainder of the trip

∴ Her speed on the remainder of the trip = x - 20 mph

∴ The remainder distance = (x - 20) × 2

∴ The remainder distance = 2x - 40 miles

∵ The total distance of the trip is 290 miles

- Equate the sum of the two distances above by 290

∴ 3x + 2x - 40 = 290

- Add the like terms in the left hand side

∴ 5x - 40 = 290

- Add 40 to both sides

∴ 5x = 330

- Divide both sides by 5

∴ x = 66

Marge drove by 66 miles per hour on the interstate

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