Question

Elisa made a trip to her friend's house and back. On the trip there she drove 75 km/h and on the return trip she went 60 km/h. How long did the trip there take if the return trip took five hours?

Answer 1

t = 4 hours

Explanation:

The distance is the same. The formula for distance is d = r*t

You could find the distance from the return trip. I'll do it that way and then take the short cut.

Method One

r = 60 km / hr

t = 5 hours

d = ?

d = r * t

d = 60 km/ hr * 5 hr The hours cancel.

d = 300 km

Now the faster trip

d = 300 km

r = 75 km

t = ??

d = r * t

300 = 75 * t Divide both sides by 75

300/75 = t

t = 4 hours.

Method Two

The distance is the same in both cases

r1 * t1 = r2 * t2

r1 = 75 km/ hr

t1 = ??

r2 = 60 km / hr

t2 = 5 hours

r1 * t1 = r2 * t2

75 * t1 = 60 * 5

75 km/hr * t1 = 60 km/hr * 5 hr

75 km / hr *t1 = 300 km Divide by 75

t1 = 300 / 75

t1 = 4 hours

Notice both methods give the same answer.