Question

На нижней полке было в 2 раза больше книг, чем на верхней. После того как на верхнюю полку по- ставили еще 12 книг, то на двух полках вместе стало 42 книги. Сколько книг было на нижней полке? ​

Answer 1

Ответ:

В нижней полке было 20 книг

Пошаговое объяснение:

Верхняя полка=x

Нижняя полка=x•2

(х+12)+х2=42

42-12=30

30=х+х2=х3

30÷3=10

х=10

х2=10•2=20

Answer 2

Problem Analysis

We are given that there are twice as many books on the bottom shelf as there are on the top shelf. After adding 12 books to the top shelf, there are a total of 42 books on both shelves combined. We need to determine the number of books on the bottom shelf.

Solution

Let's assume the number of books on the top shelf is x. According to the given information, the number of books on the bottom shelf is twice that of the top shelf, so it is 2x.

After adding 12 books to the top shelf, the total number of books on both shelves is 42. We can set up the following equation to represent this:

x + (2x) + 12 = 42

Simplifying the equation:

3x + 12 = 42

Subtracting 12 from both sides:

3x = 30

Dividing both sides by 3:

x = 10

Therefore, there were initially 10 books on the top shelf. Since the number of books on the bottom shelf is twice that of the top shelf, there were 2 * 10 = 20 books on the bottom shelf.

So, there were 20 books on the bottom shelf.

Answer

There were 20 books on the bottom shelf.