Question

Ученик прочитал 1/8 книги,а затем 2/7 оставшейся части. После этого он заметил,что прочитал на 18стр меньше,чем ему осталось прочитать.Сколько страниц в книге? Ответ должен быть 72стр

Answer 1

1 - вся книга
1-1/8=8/8-1/8=7/8 (осталось в первый раз)
7/8*2/7=2/8=1/4 (прочитал во второй раз)
1/8+1/4=1/8+2/8=3/8 (прочитал всего)
1-3/8=8/8-3/8=5/8 (осталось прочитать)
5/8-3/8=2/8=1/4 (на столько больше осталось прочитать, чем прочитал), но осталось 18 страниц, значит
18 - это 1/4 и
18 : 1/4 = 18 * 4 = 72 (страницы)
Ответ: в книге 72 страницы

Answer 2

Problem Analysis

To solve this problem, we need to determine the total number of pages in the book. We are given that the student read 1/8 of the book, then read 2/7 of the remaining part, and noticed that he read 18 pages less than what he had left to read.

Solution

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

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

After that, the student read 2/7 of the remaining part. The remaining part of the book is (7/8) * x - (1/8) * x = (6/8) * x = (3/4) * x. So, the student read (2/7) * (3/4) * x pages.

The student noticed that he read 18 pages less than what he had left to read. So, the difference between what he had left to read and what he actually read is 18 pages.

Based on the given information, we can set up the following equation:

(3/4) * x - (2/7) * (3/4) * x = 18

Simplifying the equation:

(3/4) * x - (6/28) * x = 18

(21/28) * x - (6/28) * x = 18

(15/28) * x = 18

To solve for x, we can multiply both sides of the equation by (28/15):

x = (18 * 28) / 15

x = 72

Therefore, the total number of pages in the book is 72.

Answer

The book contains 72 pages.