Grazing problem

Each window can accommodate 1 customer per minute.

1 windows, 15 minutes: 1× 15= 15 copies.

2 windows, 30 minutes reception: 2×30=60 copies.

Poor: 60- 15=45 copies.

These 45 copies are customers who arrived within 30- 15= 15 minutes.

The average number of customers per minute is: 45÷ 15=3.

In order to ensure that customers are on call, at least three windows need to be opened.

2.

The total number of science and technology books and story books in the original library was 1.

The original science and technology book is 2/(2+3)=2/5.

The storybook is 1-2/5=3/5.

Aft reading that newly bought science and technology book,

The storybook hasn't changed.

It turns out that science books are two-thirds of story books.

After purchasing new sci-tech books, the sci-tech books are storybooks 10/9.

Then the newly bought science and technology book is the original story book: 10/9-2/3=4/9.

4/9× 3/5 of the original total = 4/15.

Now the number of scientific and technological books is the original total:

2/5+4/ 15=2/3

After buying this story book,

Science and technology books remain unchanged.

Before entering the story book,

Storybook is 9/ 10 of current science and technology books.

After investing in the newly bought story book, the story book is 6/5 of the current science and technology book.

Then the newly bought story book is the current science and technology book: 6/5-9/ 10=3/ 10.

3/ 10×2/3= 1/5 of the original total.

There are more new science books than story books;

4/ 15- 1/5= 1/ 15

The original library science and technology books and story books are * * *:

100115 =1500 copies.

3.

Station 1, at least 14 people get on the bus.

Second stop, get on 13, get off 1, add 13- 1= 12.

Third stop, get on 12, get off 2, increase 12-2= 10.

The fourth stop, get on 1 1, get off 3, increase 1 1-3=8.

. . . . . .

At the seventh stop, get on 15-7=8 people, get off 7- 1=6 people, an increase of 8-6=2 people.

At the 8th stop 15-8=7 people get on the bus, and 8- 1=7 people get off, adding 0 people.

After each stop, the number of people on the bus gradually decreased.

Need a seat:

14+ 12+ 10+。 . . +2=(2+ 14)×7÷2=56.

4.

According to the meaning of the question,

A is more than 100, and b is less than 100.

The total amount spent by both parties is 2: 1.

So before the discount, the total amount of money of B is:

(2÷0.9): 1=20:9

The ratio of a to b is 5:3.

The unit price ratio of Party A and Party B is (20÷ 5): (9÷ 3) = 4: 3.

Before discount, each copy of Class A: 1.5×4/3=2 yuan.