Sita and Radha participate in a race of 1000 m. If Sita starts, when Radha has covered 100 meters, then Sita finishes the race 20 seconds before Radha, and if Sita starts, when Radha has covered 125 meters then both finish the race at the same time. How long does Sita take to run the complete race?
(A)
350
(B)
700
(C)
780
(D)
900
Answer: (B)
Explanation:
Let time taken by Sita be Ts seconds to cover 1000m.
For first case, Radha will be covering 900m is (Ts+20)sec (As it is given that Sita takes 20sec less than Radha)
So speed of Radha is (900/Ts+20) m/s
For second case, Radha will take Ts second to cover 875m (1000-125)
so speed of Radha is (875/Ts) m/s
Equating both speed of Radha we get 900Ts = 875(Ts+20) => Ts=700 sec.
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