2020 · Q38
X, Y and Z travel from the same place with uniform speeds 4 km/hr, 5 km/hr and 6 km/hr respectively. Y starts 2 hours after X. How long after Y must Z start in order that they overtake X at the same instant?
Elementary MathematicsTime, Speed and Distance
- A3/2 hours
- B4/3 hours
- C9/8 hours
- D11/8 hours
Explanation
Y catches X when 5t = 4t+8, i.e. after 8 h at 40 km. Z must satisfy 6(8-s) = 40, so s = 4/3 h after Y starts - option (B).