Question

Когда Серёжа отдал Диме треть всех своих марок, у него осталось 12 марок. Сколько марок было у Серёжи вначале?

Answer 1

12+3=9
ответ 15 парок было

Answer 2

Составим пропорцию:
12 марок - 2/3
х марок  - 1

12 : х = 2/3 : 1
х = 1*12 / 2/3 = 12 * 3/2 = 6*3 = 18.
Ответ: 18 марок.

Answer 3

Problem Analysis

We are given that Sergey gave Dima one-third of all his stamps and had 12 stamps left. We need to determine how many stamps Sergey had initially.

Solution

Let's assume that Sergey initially had x stamps.

According to the given information, Sergey gave Dima one-third of all his stamps, which is (1/3)x stamps.

After giving Dima one-third of his stamps, Sergey had 12 stamps left. So, we can set up the following equation:

x - (1/3)x = 12

Simplifying the equation, we have:

(2/3)x = 12

To find the value of x, we can multiply both sides of the equation by 3/2:

x = (12 * 3) / 2

Simplifying further, we get:

x = 18

Therefore, Sergey initially had 18 stamps.

Answer

Sergey initially had 18 stamps.

Explanation

When Sergey gave Dima one-third of his stamps, he gave away (1/3) * 18 = 6 stamps. This means that Sergey had 12 stamps left, which matches the information given in the problem statement.