Question

Перед началом представления было продано 2/5 всех воздушных шариков, а в антракте – еще 12 штук. После этого осталась половина всех шариков. Сколько шариков было первоначально?

Answer 1

1) 1-1/2=1/2 всех воздушных шаров было продано

2) 1/2-2/5=5/10-4/10=1/10 всех воздушных шаров было продано в антракте

3) 12*10=120 штук воздушных шаров было первоначально

ответ: 120 воздушных шаров

Answer 2

Problem Analysis

To solve this problem, we need to determine the initial number of balloons before the presentation. We are given the following information: - 2/5 of all balloons were sold before the presentation. - During the intermission, an additional 12 balloons were sold. - After the intermission, half of all the balloons remained.

Let's denote the initial number of balloons as 'x'. We can use this information to set up an equation and solve for 'x'.

Solution

Let's break down the information given step by step:

1. "2/5 of all balloons were sold before the presentation." - This means that 2/5 of the initial number of balloons were sold. - The remaining number of balloons is 3/5 of the initial number.

2. "In the intermission, an additional 12 balloons were sold." - This means that the remaining number of balloons decreased by 12. - The new remaining number of balloons is 3/5 of the initial number minus 12.

3. "After this, half of all the balloons remained." - This means that the new remaining number of balloons is half of the initial number. - We can set up the equation: (3/5)x - 12 = (1/2)x.

Let's solve this equation to find the initial number of balloons:

(3/5)x - 12 = (1/2)x

To get rid of the fractions, we can multiply both sides of the equation by 10:

10 * (3/5)x - 10 * 12 = 10 * (1/2)x

6x - 120 = 5x

Subtract 5x from both sides:

6x - 5x - 120 = 0

x - 120 = 0

Add 120 to both sides:

x = 120

Therefore, the initial number of balloons was 120.

Answer

The initial number of balloons before the presentation was 120.