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Places A and B are 80 km apart from each other on a highway. A car starts from A and other from B at the same time. If they move in the same direction, they meet in 8 hours and if they move in opposite direction, they meet in 1 hour and 20 minutes. Find the speeds of the cars. |
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Answer» Let’s consider the car starting from point A as X and its speed as x km/hr. And, the car starting from point B as Y and its speed as y km/hr. It’s seen that there are two cases in the question: # Case 1: Car X and Y are moving in the same direction # Case 2: Car X and Y are moving in the opposite direction Let’s assume that the meeting point in case 1 as P and in case 2 as Q. Now, solving for case 1: The distance travelled by car X = AP And, the distance travelled by car Y = BP As the time taken for both the cars to meet is 8 hours, The distance travelled by car X in 7 hours = 8x km [∵ distance = speed x time] ⇒ AP = 8x Similarly, The distance travelled by car Y in 8 hours = 8y km ⇒ BP = 8Y As the cars are moving in the same direction (i.e. away from each other), we can write AP – BP = AB So, 8x – 8y = 80 ⇒ x – y = 10 ……… (i) [After taking 8 common out] Now, solving for case 2: In this case as it’s clearly seen that, The distance travelled by car X = AQ And, The distance travelled by car Y = BQ As the time taken for both the cars to meet is 1 hour and 20 min, ⇒ 1 + (20/60) = 4/3 hr The distance travelled by car x in 4/3 hour = 4x/3 km ⇒ AQ = 4x/3 Similarly, The distance travelled by car y in 4/3 hour = 4y/3 km ⇒ BQ = 4y/3 Now, since the cars are moving in the opposite direction (i.e. towards each other), we can write AQ + BQ = AB ⇒ 4x/3 + 4y/3 = 80 ⇒ 4x + 4y = 240 ⇒ x + y = 60 …………… (ii) [After taking LCM] Hence, by solving (i) and (ii) we get the required solution From (i), we have x = 10 + y……. (iii) Substituting this value of x in (ii). ⇒ (10 + y) + y = 60 ⇒ 2y = 50 ⇒ y = 25 Now, using y = 30 in (iii), we get ⇒ x = 35 Therefore, – Speed of car X = 35 km/hr. – Speed of car Y = 25 km/hr. |
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