Question

John covered a part of his journey at 20 km/h and the remaining part at 70 km/h. It took a total of 8 hours to cover a distance of 400 km. For how long did he travel at 20 km/h?

• A. 4 h 12 min
• B. 3 h 20 min
• C. 4 h 40 min
• D. 3 h 12 min

Answer 1

The correct option is D 3 h 12 min

Distance is the product of speed and time.
The distance covered at a speed of 20 km/h, $s_1=20\times \left(T\right)$ ........ (i)

The total time taken is 8 hours.
The time to cover the remaining distance, $t_2=8-T$
The remaining distance covered at a speed of 70 km/h, $s_2=70\times (8-T)$ ....... (ii)
Given, the total distance covered, s = 400 km ....... (iii)

Also, $s=s_1+s_2$
From (i), (ii), and (iii), we get,
$400=20\times T+70\times (8-T)$
$50\times T=160$
T = 3.2 hours or 3 hours 12 minutes