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Question : Two people A and B started running from the same point on a circular track of length 400 m in opposite directions with initial speeds of 10 m/s and 40 m/s, respectively. Whenever they meet, A's speed doubles and B's speed halves. After what time from the start will they meet for the third time?

Option 1: 30 sec

Option 2: 24 sec

Option 3: 26 sec

Option 4: 28 sec


Team Careers360 3rd Jan, 2024
Answer (1)
Team Careers360 21st Jan, 2024

Correct Answer: 26 sec


Solution : Given: Total length of the track = 400 m
Speed of A = 10 m/sec
Speed of B = 40 m/sec
They are running in the opposite direction
⇒ Relative speed = 10 + 40 = 50 m/sec
We know,
Speed = $\frac{\text{Distance}}{\text{Time}}$
Time when they meet first time = $\frac{400}{50}$ = 8 sec
Now, the speed of A will get doubled and that of B will get half.
⇒ The new speed of A = 20 m/sec
And, the new speed of B = 20 m/sec
⇒ Relative speed = 20 + 20 = 40 m/sec
Time when they meet second time = $\frac{400}{40}$ = 10 sec
Now, again the speed of A will get doubled and that of B will get half.
⇒ New speed of A = 40 m/sec
And, New speed of B = 10 m/sec
⇒ Relative speed = 40 + 10 = 50 m/sec
⇒ Time when they meet third time = $\frac{400}{50}$ = 8 sec
⇒ At the third time, they will meet after 8 + 10 + 8 = 26 sec
Hence, the correct answer is 26 sec.

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