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Two trains are coming from opposite directions with speed of 75 km/hr and 100 km/hr on to parallel tracks. At some moment the distance between them is 100km. After T hours, distance between them is again 100 km. T is equal to?

11 hr
21⁷/₂ hr
31¹/₂ hr
42 hr

Answer:- 1

Explanation:-

Solution:

\begin{aligned} Relative speed \\ =  (75 + 100)km/hr \\ =  175 km/hr \\ Time taken to cover 175 km \\ at relative speed  =  1 hr \\ ∴ T  =  Time taken to cover 200 km \\ = (\frac{1}{175} \times 200) h r \\ = \frac{8}{7} h r \\ = 1 \frac{1}{7} h r \end{aligned}

$\eqalign{ & {\text{Relative speed}} \cr & {\text{ = (75 + 100)km/hr}} \cr & {\text{ = 175 km/hr}} \cr & {\text{Time taken to cover 175 km}} \cr & {\text{at relative speed = 1 hr}} \cr & \therefore {\text{T = Time taken to cover 200 km}} \cr & {\text{ = }}\left( {\frac{1}{{175}} \times 200} \right)hr \cr & = \frac{8}{7}\,hr \cr & = 1\frac{1}{7}hr \cr}$

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", "dateCreated": "7/24/2019 10:09:12 AM", "author": { "@type": "Person", "name": "Nitin Sir" } }, "suggestedAnswer": { "@type": "Answer", "text": "

Solution:

\begin{aligned} Relative speed \\ =  (75 + 100)km/hr \\ =  175 km/hr \\ Time taken to cover 175 km \\ at relative speed  =  1 hr \\ ∴ T  =  Time taken to cover 200 km \\ = (\frac{1}{175} \times 200) h r \\ = \frac{8}{7} h r \\ = 1 \frac{1}{7} h r \end{aligned}

$\eqalign{ & {\text{Relative speed}} \cr & {\text{ = (75 + 100)km/hr}} \cr & {\text{ = 175 km/hr}} \cr & {\text{Time taken to cover 175 km}} \cr & {\text{at relative speed = 1 hr}} \cr & \therefore {\text{T = Time taken to cover 200 km}} \cr & {\text{ = }}\left( {\frac{1}{{175}} \times 200} \right)hr \cr & = \frac{8}{7}\,hr \cr & = 1\frac{1}{7}hr \cr}$ ", "dateCreated": "7/24/2019 10:09:12 AM" } }

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