Riparian distance

Two ship sail in same hour the two sides that leaves a river, one sails from A toward B, another leaves for A from B, among them one leaves some more quickly than another, accordingly they are in 500 kilometers manage the bank with closer distance encounter. Arrive after booking a place, every boat should stay 15 minutes, so that let the go ashore on the passenger, next they return to base again. These two ferry are in spur another bank 100 kilometers place encounters afresh. Does river of we should like to ask have many wide?

Analysis and solve

Encounter in X dot when two ferry when, they spur A bank 500 kilometers, the distance total that right now they had taken is equal to the width of the river. When them both sides is arrived at thither when, the total length that has taken is equal to a river double wide. In return to base, they encounter in Z dot, at this moment the distance the sum that two boats had taken is equal to 3 times the river is wide, 3 times of the space that when the space that so each ferry takes now should be equal to them to encounter for the first time, takes. When two boats first time encounters, a ferry walked along 500 kilometers, arrive at Z when it so when the dot, had taken the space of 3 times, namely 1500 kilometers, this space is more than the width of the river 100 kilometers. So, the width of the river is 1400 kilometers. Of every ferry on, case of answer of time leaving a settle or live in a strange place is without an influence.

Variable exchange

Do not use any other variable, commutative A, the value of B variable?

Analysis and solve
A = A B
B = A-b
A= A-b

Walk time

The office building of some company is in downtown, and the home of company president Wensidu is in a suburb of a small town around. After he comes off work every time, be to multiply same second commuter train answers small town. Small town station leaves home to still have a paragraph of space, his private driver always is in same hour drives a car from the home, go small town station receives a president to come home. Because the train and car are very punctual, accordingly, the train and car are every time engraving a station temporarily together.

Once, the driver is compared before late half hour sets out. Wensidu arrives after the station, look for the car that is less than him, be afraid of again go back to be scolded late by wife, go to on foot along highway hurriedly go in the home, the car that he encounters in road like greased lightning and come, instantly beck signal jockeys, also do not consider after pop-up car on scold a driver, the life turns around on its horse toward answer. In returning the home, if really as expected, his wife be furious: "Go to where fool around again! You are compared answered 22 minutes late fully before... " .

Did Wensidu walk how long?

Analysis and solve

If Wen Si pauses to wait in the station all the time, so because the driver is compared before late half hours set out, accordingly, also evening half hours reach a station. That is to say, wensidu will be in station cool one's heels half hours, the car sits to come home after the car that waits for him arrives, thereby he will be compared before evening arrives home half hours. And Wensidu arrives home 22 minutes late than ever only now, this shortens if the president waits to death in the railway station,8 minutes when come down are, the driver wants a flower to go to a railway station to return the time on this place again in the place that encounters Wensidu's president from now originally. This is meant, if the driver drives to hurry to a railway station from the place that encounters a president now, the time that one-way place spends will be 4 minutes. Accordingly, if Wen Si pauses,wait in the railway station, pass 4 minutes again, his car also arrived. That is to say, if he waits be in a railway station, so he also had waited for 30-4=26 minute. But henpecked Wensidu's president did not wait after all, he hurries on with his journey impatiently, getting on flower of these 26 minutes of all on foot.
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