Question

На столе лежала пачка тетрадей. Сначала взяли 30% этих тетрадей, а потом 75% оставшихся тетрадей. После этого на столе осталось 14 тетрадей. Сколько тетрадей было в пачке первоначально?

Answer 1

Решаем задачу с конца
1) 14 тетрадей = 25%
х = 100 %  ( 25, потому что взяли 75%)
х = 56 тетрадей
2) 56 т. = 70% (потому что взяли 30%)
    у = 100%
у = 80 тетрадей было первоначально
от них забрали 30% = 24 т
80 - 24 = 56т
от 56 забрали 75% = 42т
56 - 42 = 14 т.
Ответ: 80 тетрадей

Answer 2

14 - 25%
x - 75%
x=42

42 - 70%
a - 30 %
a=18

42+18=60

ответ : 60

Answer 3

Problem Analysis

We are given that there was a pack of notebooks on a table. First, 30% of these notebooks were taken, and then 75% of the remaining notebooks were taken. After this, there were 14 notebooks left on the table. We need to determine the initial number of notebooks in the pack.

Solution

Let's assume the initial number of notebooks in the pack is x.

According to the problem, the following steps were taken: 1. First, 30% of the notebooks were taken. This means that 70% of the notebooks remained. 2. Then, 75% of the remaining notebooks were taken. This means that 25% of the notebooks remained.

We can express these steps mathematically as follows:

Step 1: 0.7x notebooks remained after taking 30% of the initial notebooks. Step 2: 0.25(0.7x) notebooks remained after taking 75% of the remaining notebooks.

According to the problem, there were 14 notebooks left on the table after these steps. So we can set up the equation:

0.25(0.7x) = 14

To find the value of x, we can solve this equation.

Calculation

Let's solve the equation:

0.25(0.7x) = 14

First, simplify the equation:

0.175x = 14

Now, isolate x by dividing both sides of the equation by 0.175:

x = 14 / 0.175

Evaluating the right side of the equation:

x = 80

Answer

The initial number of notebooks in the pack was 80.

Explanation

Initially, there were 80 notebooks in the pack. 30% of 80 is 24, so 24 notebooks were taken. This left 56 notebooks on the table. Then, 75% of 56 is 42, so 42 notebooks were taken. This left 14 notebooks on the table, which matches the information given in the problem. Therefore, the initial number of notebooks in the pack was 80.