$$ 50 \quad $$ A man drove for 4hours at a certain speed, he then doubled his speed and drove for another 3 hours. Altogether he covered 600 km . At what speed did he drive for the last 3 hours? $$ \begin{array}{lll} ext { A. } 120 \mathrm{~km} / \mathrm{hr} & ext { B. } 60 \mathrm{~km} / \mathrm{hr} & ext { C. } 600 / 7 \mathrm{~km} / \mathrm{hr} \ ext { D. } 50 \mathrm{~km} / \mathrm{hr} & ext { E. } 100 \mathrm{~km} / \mathrm{hr}\end{array} $$

Question

$$ 50 \quad $$ A man drove for 4hours at a certain speed, he then doubled his speed and drove for another 3 hours. Altogether he covered 600 km . At what speed did he drive for the last 3 hours? $$ \begin{array}{lll}	ext { A. } 120 \mathrm{~km} / \mathrm{hr} & 	ext { B. } 60 \mathrm{~km} / \mathrm{hr} & 	ext { C. } 600 / 7 \mathrm{~km} / \mathrm{hr} \ 	ext { D. } 50 \mathrm{~km} / \mathrm{hr} & 	ext { E. } 100 \mathrm{~km} / \mathrm{hr}\end{array} $$

UpStudy AI · Accepted Answer

Let's solve the problem step by step.

**Given:**
- The man drove for 4 hours at a certain speed, $$ v $$ km/hr.
- He then doubled his speed to $$ 2v $$ km/hr and drove for another 3 hours.
- The total distance covered is 600 km.

**Step 1: Calculate the distance covered at each speed.**
- **First segment:** 
  $$
  \text{Distance} = \text{Speed} \times \text{Time} = v \times 4 = 4v \, \text{km}
  $$
  
- **Second segment:**
  $$
  \text{Distance} = \text{Speed} \times \text{Time} = 2v \times 3 = 6v \, \text{km}
  $$

**Step 2: Sum the distances and set equal to the total distance.**
$$
4v + 6v = 600 \, \text{km}
$$
$$
10v = 600
$$

**Step 3: Solve for $$ v $$.**
$$
v = \frac{600}{10} = 60 \, \text{km/hr}
$$

**Step 4: Determine the speed during the last 3 hours.**
$$
\text{Doubled speed} = 2v = 2 \times 60 = 120 \, \text{km/hr}
$$

**Answer:**  
**A. 120 km/hr**
He drove at 120 km/hr for the last 3 hours.

A man drove for 4hours at a certain speed, he then
doubled his speed and drove for another 3 hours.
Altogether he covered 600 km . At what speed did he
drive for the last 3 hours?

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