Question

Ученик прочитал одну восьмую книги,а затем две седьмых оставшейся части. После этого он заметил, что прочитал на 18 страниц меньше, чем ему осталось прочитать. Сколько страниц в книге?

Answer 1

Х - вся книга.
1/8х - прочитал сначала.
х - 1/8х - осталось.
(х - 1/8х)* 2/7 = 2/7х - 1/28х - прочитал второй раз.
1/8х + 2/7х - 1/28х = 3/8х - всего прочитал за два раза. 
х - 3/8х = 5/8х - осталось прочитать.

5/8х - 3/8х = 18
1/4х = 18
х = 18 : 1/4
х = 72 стр - в книге.

Answer 2

Problem Analysis

The student read one-eighth of the book, then two-sevenths of the remaining part. After that, the student noticed that they had read 18 pages less than what was left to read. We need to determine the total number of pages in the book.

Solution

Let's assume the total number of pages in the book is x.

The student read one-eighth of the book, which is (1/8)x pages.

The remaining part of the book is x - (1/8)x = (7/8)x pages.

The student then read two-sevenths of the remaining part, which is (2/7)(7/8)x = (1/4)x pages.

According to the problem, the student read 18 pages less than what was left to read. So, we can set up the equation:

(1/4)x = (7/8)x - 18

To solve this equation, we can multiply both sides by 8 to eliminate the fractions:

2x = 7x - 144

Simplifying further:

5x = 144

Dividing both sides by 5:

x = 28.8

Since the number of pages in a book cannot be a decimal, we can round it to the nearest whole number:

x ≈ 29

Therefore, the book has approximately 29 pages.

Answer

The book has approximately 29 pages.