Question

Рыбак поймал на рыбалке 20 карпов, из которых 60% оказались обычными, а остальные зеркальными. Затем часть зеркальных карпов рыбак отпустил, после чего обычные карпы составили уже 80% от всей пойманной рыбы. Сколько всего карпов осталось у рыбака?

Answer 1

1) 0,6*20 = 12 (карпов) - обычных
2) 12/0,8 = 15 (карпов) - осталось всего

Ответ: 15 карпов

Answer 2

Problem Analysis

The fisherman caught 20 carp during his fishing trip. Out of these, 60% were ordinary carp, and the rest were mirror carp. After releasing some mirror carp, the proportion of ordinary carp in the total catch increased to 80%. We need to determine how many carp the fisherman has left.

Solution

Let's start by calculating the initial number of mirror carp and ordinary carp caught by the fisherman.

The fisherman caught 20 carp in total. Let's represent the number of ordinary carp as x and the number of mirror carp as y.

According to the problem, 60% of the carp caught were ordinary carp. So we can write the equation:

x = 0.6 * 20

Simplifying, we find:

x = 12

Therefore, the fisherman caught 12 ordinary carp.

The remaining carp are mirror carp, so we can write the equation:

y = 20 - x

Substituting the value of x, we find:

y = 20 - 12

Simplifying, we find:

y = 8

Therefore, the fisherman caught 8 mirror carp.

Now, let's calculate the number of carp the fisherman has left after releasing some mirror carp.

The proportion of ordinary carp in the total catch increased to 80%. Let's represent the number of ordinary carp left as a and the number of mirror carp left as b.

According to the problem, the proportion of ordinary carp is now 80%. So we can write the equation:

a / (a + b) = 0.8

Simplifying, we find:

a = 0.8 * (a + b)

Expanding, we find:

a = 0.8a + 0.8b

Simplifying further, we find:

0.2a = 0.8b

Dividing both sides by 0.2, we find:

a = 4b

Now, let's substitute the values of a and b to find the number of carp the fisherman has left.

a = 4 * 8

Simplifying, we find:

a = 32

Therefore, the fisherman has 32 carp left.

Answer

The fisherman has 32 carp left.