Предмет: Алгебра, автор: margarita04mn

скорость одного велосипедиста на 4 км/ч больше скорости другого, поэтому он за 3 часа проезжает но 5 км больше ,чем другой за 3,5 часа. С какой скоростью двигается каждый веласипедист?

Ответы

Автор ответа: ubgh

Пусть х км/ч - скорость велосипедиста

(4+х)*3= 3,5х+5

12+3х=3,5х+5
0,5х=7
Х=14

Скорость первого 18, второго 14

margarita04mn: спс

ubgh: не за что)

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Operation Migration

If you look up at the sky in the early autumn in the northern part of North America, you may see groups of birds. These birds are flying south to places where they can find food and warmth for the winter. They are migrating. The young birds usually learn to migrate from their parents. They follow their parents south. In one unusual case, however, the young birds are following something very different. These birds are young wooping cranes, and they are following an airplane!
The wooping crane is the largest bird that is native to North America. These birds almost disappeared in the 1800s. By 1941, there were only about 20 cranes alive. In the 1970s, people were worried that these creatures were in danger of disappearing completely. As a result, the United States identified wooping cranes as an endangered species that they needed to protect.
Some researches tried to help. They began to breed wooping cranes in special parks to increase the number of birds. This plan was successful. There were a lot of new baby birds. As the birds became older, the researchers wanted to return them to nature. However, there was a problem: these young birds did not know how to migrate. They needed human help.
In 2001, some people had a creative idea. They formed an organization called Operation Migration. This group decided to use very light airplanes, instead of birds, to lead the young wooping cranes on their first trip south. They painted each airplane to look like a wooping crane. Even the pilots wore special clothing to make them look like cranes. The cranes began to trust the airplanes, and the plan worked.
Today, planes still lead birds across approximately 1, 930 kilometres, from the United States – Canadian border to the Gulf of Mexico. They leave the birds at different sites. If a trip is successful, the birds can travel on their own in the future. Then, when these birds become parents, they will teach their young to migrate. The people of Operation Migration think this is the only way to maintain the wooping crane population.
Operation Migration works with several other organizations and government institutes. Together, they assist hundreds of cranes each year. However, some experts predict that soon, this won’t be necessary. Thanks to Operation Migration and its partners, the crane population will continue to migrate. Hopefully, they won’t need human help anymore.

1. Put down + if the statement is true, - if it is false (2 points each).

1) Young birds usually learn to migrate from their parents.
2) Wooping cranes almost vanished in the 1800s.
3) In the 1970s, people worried that there were too many wooping cranes.
4) Wooping cranes needed to be protected because they were given a conservation status.
5) Thanks to the researchers, wooping cranes were successfully bred in special gardens.
6) People had to teach the wooping cranes how to migrate.
7) Operation Migration uses light trucks to transport the wooping cranes.
8) Today, only with the help of light airplanes we are able to maintain the wooping crane population.
9) Migration specialists predict that soon wooping cranes will not need human help to migrate.

2. Choose the correct letter (a, b or c) – (2 points each)
10) Wooping cranes migrate in the winter to find ………….
a) baby wooping cranes
b) warmth and food
c) human help

11)Wooping cranes are native to ….
a) Mexico
b) South America
c) North America

12) What does Operation Migration do?
a) They teach adult cranes how to fly.
b) They lead young cranes on their first trip south.
c) They breed cranes in special parks.

13) Approximately how many kilometers is the wooping crane’s trip from north to south?
a) 1, 930 kilometres
b) 1, 913 kilometres
c) 1, 900 kilometres

14) If Operation Migration is successful, what will happen?
a) Wooping cranes will follow airplanes south every year.
b) Wooping cranes will learn to migrate on their own.
c) Wooping cranes will learn to live in Canada all year.
3. Write short answers to the following questions (3 points each)

15) How many whooping cranes were there in 1941? ______________________________________________
16) Why couldn’t researchers return the young birds to nature? ______________________________________________
17) Why do the cranes trust the airplanes and the pilots? _______________________________________________
18) Why do some people predict that Operation Migration will stop soon?

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