CAT 2017 Slot 2QA Question 4

Basics of TSD/ProportinalityEasy

Arun drove from home to his hostel at 60 miles per hour. While returning home he drove half way along the same route at a speed of 25 miles per hour and then took a bypass road which increased his driving distance by 5 miles, but allowed him to drive at 50 miles per hour along this bypass road. If his return journey took 30 minutes more than his onward journey, then the total distance traveled by him is

Answer & solution

Correct answer: 65 miles

  • A

    55 miles

  • B

    60 miles

  • 65 miles

  • D

    70 miles

Solution

Easy

Let the one-way distance be dd. Write the onward time and the (longer) return time, set return == onward +12+\tfrac12 hour, solve for dd, then add up every leg actually driven.

1

Onward time. The full distance dd at 6060 mph.

tonward=d60\begin{aligned} &t_{\text{onward}}=\frac{d}{60} \end{aligned}
2

Return time. First half d2\tfrac{d}{2} at 2525 mph, then the bypass of length d2+5\tfrac{d}{2}+5 at 5050 mph.

treturn=d/225+d/2+550 treturn=d50+d100+110=3d+10100\begin{aligned} &t_{\text{return}}=\frac{d/2}{25}+\frac{d/2+5}{50}\\ &\Rightarrow\ t_{\text{return}}=\frac{d}{50}+\frac{d}{100}+\frac{1}{10}=\frac{3d+10}{100} \end{aligned}
3

Apply the 3030-minute gap. Return exceeds onward by 12\tfrac12 hour.

3d+10100=d60+12 3(3d+10)=5d+150(×300) 9d+30=5d+150 4d=120  d=30\begin{aligned} &\frac{3d+10}{100}=\frac{d}{60}+\frac{1}{2}\\ &\Rightarrow\ 3(3d+10)=5d+150 \quad\text{(}\times300\text{)}\\ &\Rightarrow\ 9d+30=5d+150\\ &\Rightarrow\ 4d=120\ \Rightarrow\ d=30 \end{aligned}
4

Total distance driven. Onward dd, plus return d2+(d2+5)\tfrac{d}{2}+\bigl(\tfrac{d}{2}+5\bigr).

Total=d+d2+d2+5=2d+5 2(30)+5=65 miles\begin{aligned} &\text{Total}=d+\frac{d}{2}+\frac{d}{2}+5=2d+5\\ &\Rightarrow\ 2(30)+5=65\ \text{miles} \end{aligned}
Total distance=65 miles\text{Total distance}=65\ \text{miles}

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CAT 2017 Slot 2 QA Q4: Arun drove from home to his hostel at 60 miles per hour. While returning home he drove half way along the same — Solution | TheCATExam