Running 20% slower, a train would take 45 minutes more for a 180 km trip. At its normal speed, how long does this 300 m train take to cross a 450 m bridge?

Question

Accepted Answer

45 s. At 80% speed time becomes 1.25T: 0.25T=0.75 h → T=3 h, speed =60 km/h =50/3 m/s. Bridge: 750÷50/3=45 s. (56.25 s uses the slower 48 km/h.)

Running 20% slower, a train would take 45 minutes more for a 180 km trip. At its normal speed, how long does this 300 m train take to cross a 450 m bridge?

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