Question

When Fritz drives to work his trip takes 35 minutes, but when he takes the train it takes 15 minutes. Find the distance Fritz travels to work if the train travels an average of 80 miles per hour faster than his driving. Assume that the train travels the same distance as the car.

Answer 1

35 miles

Explanation:

Let's say Fritz travels at x miles per hour via train and y miles per hour via car.

(speed of car) + 80 miles per hour = speed of train

y + 80 = x

Speed * time = distance

Speed of train * time of train = distance = speed of car * time of car

x * 15 minutes = y * 35 minutes

convert minutes to hours since miles per hour is in terms of hours

60 minutes = 1 hour

15 minutes = ? hours

multiply 15 minutes by 1 hour/60 minutes. since 60 minutes = 1 hour, we can divide both sides by 60 minutes to get 1 hour/60 minutes = 1. we can always multiply by 1, so we do that here. note that the minutes are in the denominator so the 15 minutes cross out with the 60 minutes, leaving us with only hours as our unit.

15 minutes = 15 minutes * 1 = 15 minutes * 1 hour/60 minutes = 15/60 hours = 3/12 hours

similarly, 35 minutes * 1 hour/60 minutes = 35/60 hours = 7/12 hours

x * 15 minutes = y * 35 minutes

x * 3/12 hours = y * 7/12 hours

plug y+80 in for x

(y+80) * 3/12 hours = y * 7/12 hours

(3/12) * y + 20 = (7/12) * y

subtract (3/12) * y from both sides to isolate the variable (y) and its coefficient

20 = (4/12) * y

multiply both sides by 12/4 (the inverse of the coefficient) to get rid of the coefficient

20*12/4 = y = 60

y = 60 miles per hour

x = y + 80 = 140 miles per hour

distance = x * 3/12 hours = 140 miles/hour * 3/12 hours= 35 miles