A train passes a 900 meter long railway bridge. It takes 1 minute and 25 seconds from the front of the train to the rear of the train to leave the bridge. Then the train goes through a 1800 meter long tunnel. It takes 2 minutes and 40 seconds from the front of the train to the rear of the train to leave the tunnel

A train passes a 900 meter long railway bridge. It takes 1 minute and 25 seconds from the front of the train to the rear of the train to leave the bridge. Then the train goes through a 1800 meter long tunnel. It takes 2 minutes and 40 seconds from the front of the train to the rear of the train to leave the tunnel

1 minute 25 seconds = 85 seconds, 2 minutes 40 seconds = 160 seconds, train speed is: (1800-900) / (160-85), = 900 / - 75, = 12 (M / s); body length is: 85 × 12-900, = 1020-900, = 120 (m); answer: train speed is 12 m / s, body length is 120 M

A railway is one kilometer long. There is a train passing through. It takes one minute from the beginning to the end of the train. It takes 40 seconds from the end of the train to the end of the train
Simple and clear
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A family of three, husband. wife. Son. The sum of their ages is 68. Their husband is three years older than their wife. Four years ago, the sum of their ages was 57. What is the age of each member of the family?

1. Suppose the length of the train is a, the equation is: (1000 + a) / 60 = (1000-a) / 40, the solution is: a = 200m, the speed of the train is v = (1000 + 200) / 60 = 20m / S = 72km / H 2, because the sum of the three people's ages four years ago is 57 years old, and now is 68 years old, we can know that the son's age is less than 4 years old, let the wife's age be x years old

It takes 21 seconds for a fire to pass a 120 meter bridge and 17 seconds for a fire to pass an 80 meter bridge

Let the train be x meters long and Y meters fast
120+X=21Y
80+X=17Y
The answer is x = 90, y = 10
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