At 3pm Ellen headed north at 30 kilometers per hour Two hours later Tom headed south at 40 kilometers per hour At what time will they be 340 kilometers apart?

Answer 1

Let t be the amount of time before Ellen and Tom are 340 miles apart.

In this time, Ellen traveled 30t miles

Tom started 2 hours later, so he traveled 40(t-2) miles

Together they traveled 30t + 40(t-2) = 340 miles

solving for t: 70t - 80 = 340, 70t = 420, t =6

So in 6 hours, they will be 340 miles apart

Without algebra. When Tom started his southward journey at 5pm they were 60Km apart. After that they moved apart by 30Km+ 40Km, so by 70Km/hr. Four hours from 5pm they would be an additional 280Km apart; (70x 4). Add the distance between them and it will be 280km+60Km. Figures are all whole numbers and easy to deal with, thus it can easily be solved mentally.