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Ted and Robin start from the same point at 7 AM and drive in opposite directions. Ted doubles his speed after every 90 minutes whereas Robin reduces her speed by half after every 120 minutes. If Ted starts driving at a speed of 10 kilometers/hour and Robin starts driving at a speed of 120 kilometers/hour, how far in kilometers will they be from one another at 1 PM?
  • a)
    195
  • b)
    485
  • c)
    525
  • d)
    645
  • e)
    675
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
Ted and Robin start from the same point at 7 AM and drive in opposite ...
Given
  • Ted starts at 7 AM
    • Ted’s initial speed = 10 kilometers/hour
    • Ted doubles his speed after every 1.5 hours
 
  • Robin starts at 7 AM from the same point as Ted and travels in opposite directions
    • Robin’s initial speed = 120 kilometers/hour
    • Robin reduces her speed by half after every 2 hours
To Find: Distance between Ted and Robin at 1 PM
  • Find the distance travelled by Ted in 6 hours
  • Find the distance travelled by Robin in 6 hours
 
Approach
Distance = Speed * Time
1. We need to find the distance travelled by Ted in 6 hours As Ted doubles his speed after every 1.5 hours, he will travel at 6/1.5=4
  1.  different speeds during the period
  2. We know his initial speed and we know that he doubles his speed after every interval of 1.5 hours. So, we can calculate his speed for each interval
 
2.  We need to find the distance travelled by Robin in 6 hours
  1. As Robin reduces her speed after every 2 hours, she will travel at 6/2=3
  1.  different speeds during the period
  2. We know her initial speed and we know that she reduces her speed by half after every interval of 2 hours. So, we can calculate her speed for each interval.
 
Working Out
1.  Ted 
2.  Robin
Distance between Ted and Robin at 1 PM = 225 + 420 = 645 kilometers
Answer: D
View all questions of this test
Most Upvoted Answer
Ted and Robin start from the same point at 7 AM and drive in opposite ...
To solve this problem, we need to calculate the distances covered by Ted and Robin separately and then find the sum of their distances.

Ted's journey:
Ted doubles his speed after every 90 minutes. So, he will have different speeds during different time intervals.

From 7 AM to 8:30 AM (90 minutes):
Ted's speed = 10 km/hour
Distance covered = Speed × Time = 10 km/hour × 1.5 hours = 15 km

From 8:30 AM to 10 AM (90 minutes):
Ted's speed = 2 × 10 km/hour = 20 km/hour
Distance covered = Speed × Time = 20 km/hour × 1.5 hours = 30 km

From 10 AM to 11:30 AM (90 minutes):
Ted's speed = 2 × 20 km/hour = 40 km/hour
Distance covered = Speed × Time = 40 km/hour × 1.5 hours = 60 km

From 11:30 AM to 1 PM (90 minutes):
Ted's speed = 2 × 40 km/hour = 80 km/hour
Distance covered = Speed × Time = 80 km/hour × 1.5 hours = 120 km

Total distance covered by Ted = 15 km + 30 km + 60 km + 120 km = 225 km

Robin's journey:
Robin reduces her speed by half after every 120 minutes. So, she will have different speeds during different time intervals.

From 7 AM to 9 AM (120 minutes):
Robin's speed = 120 km/hour
Distance covered = Speed × Time = 120 km/hour × 2 hours = 240 km

From 9 AM to 11 AM (120 minutes):
Robin's speed = 120 km/hour ÷ 2 = 60 km/hour
Distance covered = Speed × Time = 60 km/hour × 2 hours = 120 km

From 11 AM to 1 PM (120 minutes):
Robin's speed = 60 km/hour ÷ 2 = 30 km/hour
Distance covered = Speed × Time = 30 km/hour × 2 hours = 60 km

Total distance covered by Robin = 240 km + 120 km + 60 km = 420 km

Total distance between Ted and Robin at 1 PM = Distance covered by Ted + Distance covered by Robin = 225 km + 420 km = 645 km

Therefore, the correct answer is option D) 645 km.
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Ted and Robin start from the same point at 7 AM and drive in opposite directions. Ted doubles his speed after every 90 minutes whereas Robin reduces her speed by half after every 120 minutes. If Ted starts driving at a speed of 10 kilometers/hour and Robin starts driving at a speed of 120 kilometers/hour, how far in kilometers will they be from one another at 1 PM?a)195b)485c)525d)645e)675Correct answer is option 'D'. Can you explain this answer?
Question Description
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