Mathematical Reasoning
Town A and Town B are 900 kilometres apart. A car that travels at 80 kilometres per hour leaves Town A for To…
Question 1 · Multiple choice
Question
Town A and Town B are 900 kilometres apart. A car that travels at 80 kilometres per hour leaves Town A for Town B. At the same time, another car leaves Town B for Town A at 70 kilometres per hour. When will the two cars meet?
Options
- A.6 hours
- B.5 hours
- C.4.5 hours
- D.7 hours
- E.8 hours
Correct answer
Explanation
Step 1: Understand the situation
The two cars leave at the same time and drive toward each other. Together, they are closing the 900 km gap between them.
Town A ────────────────────────────── Town B
Car 1 ──▶ 80 km/h 70 km/h ◀── Car 2
They meet somewhere here!
Step 2: Find the combined closing speed
Since both cars move toward each other, their speeds add together:
Combined speed = 80 + 70 = 150 km/h
Think of it this way: every hour, Car 1 covers 80 km and Car 2 covers 70 km, so together they cover 150 km of the 900 km gap.
Step 3: Find the time until they meet
Time = Distance ÷ Speed = 900 ÷ 150 = 6 hours
Check: After 6 hours, Car 1 has travelled 80×6 = 480 km, Car 2 has travelled 70×6 = 420 km. Total = 480 + 420 = 900 km ✓
Answer: They meet after 6 hours
| Option | Value | Why it is wrong |
|---|---|---|
| A | 6 hours | 900 ÷ 150 = 6. ✓ |
| B | 5 hours | Used only one car's speed. ✗ |
| C | 4.5 hours | Arithmetic error. ✗ |
| D | 7 hours | Used 900 ÷ 80 + something incorrectly. ✗ |
| E | 8 hours | Used 900 ÷ 80 alone (too slow). ✗ |