Question

На полке стояли книги. Сначала с полки взяли 25% всех книг, а потом 70% оставшихся книг. После этого на полке осталось 27 книг. Сколько было на полке книг первоначально?

Answer 1

Вы ошибаетесь.

Правильное решение:

Смотрите, 27 книг у вас будут являться 30% (100%-70%), соответственно, в 100% будет 90 книг. Теперь поднимемся выше. 90 книг - это 75% (сняли же 25%), и получаем, что изначально было 120 книг ((90/75)*100). Все просто)

Answer 2

Problem Analysis

We are given the following information: - Initially, there were some books on a shelf. - 25% of all the books were taken from the shelf. - Then, 70% of the remaining books were taken from the shelf. - After this, there were 27 books left on the shelf.

We need to determine the initial number of books on the shelf.

Solution

Let's assume the initial number of books on the shelf is x.

According to the given information: - 25% of all the books were taken from the shelf, which means 75% (100% - 25%) of the books remained on the shelf. - Then, 70% of the remaining books were taken from the shelf, which means 30% (100% - 70%) of the books remained on the shelf. - After this, there were 27 books left on the shelf.

We can set up the following equation to solve for x:

0.3 * 0.75 * x = 27

Simplifying the equation:

0.225 * x = 27

Dividing both sides of the equation by 0.225:

x = 27 / 0.225

Calculating the value of x:

x = 120

Therefore, the initial number of books on the shelf was 120.

Answer

The initial number of books on the shelf was 120.