A car travels at a speed of 24 km/hr and covers a distance of 84 km. After that, the car increases its speed by 25% and covers the next 150 km. What is the total time taken for the entire journey?
- AOption (a)
8.5 hours
- BOption (b)
9.25 hours
- COption (c)
10.75 hours
- DOption (d)
11.5 hours
- EOption (e)
None of these
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Correct answer
8.5 hours
Why this answer is correct
Shortcut Trick
First part time = 84 ÷ 24 = 3.5 hr
New speed = 24 × 1.25 = 30 km/hr
Second part time = 150 ÷ 30 = 5 hr
Total time = 3.5 + 5 = 8.5 hr
∴ The correct answer is 8.5 hr.
Alternate Method
Given: First distance (D1) = 84 km, First speed (S1) = 24 km/hr, Second distance (D2) = 150 km.
Formula Used: Time = Distance ÷ Speed
⇒ Time for first part (T1) = D1 ÷ S1
⇒ T1 = 84 ÷ 24 = 3.5 hr
⇒ Increased speed (S2) = S1 + (25% of S1)
⇒ S2 = 24 + (25/100 × 24) = 24 + 6 = 30 km/hr
⇒ Time for second part (T2) = D2 ÷ S2
⇒ T2 = 150 ÷ 30 = 5 hr
⇒ Total Time = T1 + T2 = 3.5 + 5 = 8.5 hr
∴ The correct answer is 8.5 hr.
Additional Information
Average Speed Formula
Average Speed = Total Distance ÷ Total Time. For this journey, Average Speed = (84 + 150) ÷ 8.5 ≈ 27.53 km/hr.
Percentage Increase in Speed
When speed increases by x%, the new speed is S × (1 + x/100). Here, 24 × (1 + 0.25) = 24 × 1.25 = 30 km/hr.
Unit Conversion
To convert km/hr to m/s, multiply by 5/18. To convert m/s to km/hr, multiply by 18/5.