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Places A and B are 100 km apart from each other on a highway. A car starts from A another from B at the same time. If they move in the same direction, they meet in 10 hours and if they move in opposite direction, they meet in 1 hour 40 minutes. Find the speed of the cost from places A and B respectively are : 

(a) 45 km/hr, 25 km/hr 

(b) 65 km/hr, 75 km/hr 

(c) 35 km/hr, 25 km/hr 

(d) 60 km/hr, 45 km/hr

1 Answer

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Best answer

(c) 35 km/hr, 25 km/hr

Let X and Y be two cars starting from points A and B respectively.

Let the speed of the car X be x km/hr and that of car Y be y km/hr.

Case I : When the two cars move in the same direction.

Suppose the two cars meet at point P after 10 hours.

Then, Dist. travelled by car X = AP = 10x km 

and Dist. travelled by car Y = BP = 10y km 

Given, AP – BP = AB

\(\Rightarrow\) 10x – 10y = 100 \(\Rightarrow\) x – y = 10 ...........(i)

Case II: When the two cars move in the opposite direction :

Suppose the two cars meet at point Q of 1 hrs

40 min = 1\(\frac{40}{60}\)hrs = 1\(\frac{2}{3}\)hrs= \(\frac{5}{3}\)hrs.

Then, dist. travelled by car X = AQ =\(\frac{5X}{3}\)km

and dist. travelled by car Y = BQ = \(\frac{5y}{3}\)km

Given, AQ + BQ = 100

\(\Rightarrow\) \(\frac{5X}{3}\) + \(\frac{5y}{3}\) = 100

\(\Rightarrow\) (x+y) = \(\frac{300}{5}\) = 60 ...........(ii)

Adding (i) and (ii)

2x = 70

\(\Rightarrow\) x = 35

\(\therefore\) From (i), 35 – y = 10 \(\Rightarrow\) y = 25 km/hr

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