Question

3. Имеется кусок сплава меди с оловом массой 25 кг, содержащий 20% меди. Сколько чистой меди надо добавить к этому сплаву, чтобы новый сплав содержал 40% олова?

Answer 1

Ответ:

Пошаговое объяснение:

пусть-х - масса меди

пусть-у - масса олова

х кг - 20%

15 кг - 100%

х = 0,2 * 15 = 3 кг - меди в сплаве

у = 12 кг - олова в сплаве

12 кг - 40%

медь кг - 100%

медь = 12 * 100 : 40 = 30 кг - масса сплава, где олова будет 40% (масса олова не изменяется)

масса меди в новом сплаве х = 30 - 12 = 18 кг

другая массы меди х - х = 18 - 3 = 15 кг

Answer 2

Ответ:

Пошаговое объяснение:

100%=25

20%=х

Х=25×20÷100=5кг меди в сплава

25-5=20кг олова

20% 5 кг

40% х

Х=5÷20×40=10кг

10-5=5кг меди надо добавить

Answer 3

Problem Analysis

We have a copper-lead alloy weighing 25 kg, which contains 20% copper. We need to determine how much pure copper needs to be added to this alloy to create a new alloy containing 40% lead.

Solution

To solve this problem, we can use the concept of mass conservation. The total mass of the alloy before and after adding pure copper should remain the same.

Let's denote the mass of the pure copper to be added as x kg.

The mass of copper in the original alloy is 20% of 25 kg, which is 5 kg. The mass of lead in the original alloy can be calculated as the difference between the total mass and the mass of copper:

Mass of lead in the original alloy = Total mass - Mass of copper Mass of lead in the original alloy = 25 kg - 5 kg = 20 kg

After adding x kg of pure copper, the total mass of the alloy will be 25 kg + x kg.

The mass of copper in the new alloy will be the sum of the mass of copper in the original alloy (5 kg) and the mass of pure copper added (x kg).

The mass of lead in the new alloy will be the difference between the total mass and the mass of copper in the new alloy.

We want the new alloy to contain 40% lead. This means that the mass of lead in the new alloy should be 40% of the total mass of the new alloy.

Now we can set up an equation to solve for x:

Mass of lead in the new alloy = 40% of (Total mass of the new alloy) 20 kg + (25 kg + x kg) = 0.4 * (25 kg + x kg)

Simplifying the equation:

20 kg + 25 kg + x kg = 0.4 * 25 kg + 0.4 * x kg 45 kg + x kg = 10 kg + 0.4 x kg

Subtracting 0.4 x kg from both sides:

45 kg + x kg - 0.4 x kg = 10 kg

Simplifying further:

0.6 x kg = 35 kg

Dividing both sides by 0.6:

x kg = 35 kg / 0.6 x kg ≈ 58.33 kg

Therefore, approximately 58.33 kg of pure copper needs to be added to the alloy to create a new alloy containing 40% lead.

Answer

Approximately 58.33 kg of pure copper needs to be added to the alloy to create a new alloy containing 40% lead.