17. Places A and B are 80 km apart from each other on a highway. A car starts from A and
another from B at the same time. If they move in same direction they meet in 8 hrs and if
they move in opposite directions they meet in 1 hr 20 minutes. Find speeds of the cars.
Answers
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Answer-
Speed of car A = 35 km/hr and B = 25 km/hr
Step-by-step explanation-
Let the speed of car which starts from A be x km/hr and B be y km/hr.
Case 1)
Places A and B are 80 km apart from each other on a highway. A car starts from A and another from B at the same time. If l they move in same direction they meet in 8 hrs.
Time = 8 hrs and distance = 80 km
Both cars are moving in same direction. So, speed = (x - y) km/hr
Time = Distance/Speed
⇒ 8 = 80/(x - y)
⇒ x - y = 80/8
⇒ x - y = 10
⇒ x = 10 + y
Case 2)
If both cars move in opposite direction then they meet in 1 hr 20 min.
Now, speed = (x + y) km/hr
Time = 1 hr 20 min = (1 + 20/60) = 4/3 hrs.
Distance = 80 km
⇒ 4/3 = 80/(x + y)
⇒ x + y = (80 × 3)/4
⇒ x + y = 60
From above we can write it like,
⇒ 10 + y + y = 60
⇒ 2y = 50
⇒ y = 25 km/hr
Substitute value of y in x
⇒ x = 10 + 25
⇒ x = 35 km/hr