Question

Черные лебеди составляют 40% от числа черных и белых лебедей, живущих в заповеднике. Сколько черных лебедей, если белых лебедей на 21 больше, чем черных?

Answer 1

Кол-во чёрных лебедей=х
кол-во белых лебедей=у
х=0.4*(x+y)
0.6x=0.4y
y=1.5x
значит 1,5х-х=21
            х=42 чёрных лебедя

Answer 2

100%-40%=60% белых лебедей  в заповедники
60%-40%=20% на 20% от всего количества больше белых лебедей
дальше создаём пропорцию
х=40%
21=20%
и решаем её
х/21=40/20
20х=840
х=42 черных лебедя в заповеднике
Ответ 42 чёрных лебедя  в заповедники

Answer 3

Calculating the Number of Black Swans

To calculate the number of black swans, we can use the information provided and solve for the number of black swans.

Given: - Black swans constitute 40% of the total number of black and white swans in the reserve. - The number of white swans is 21 more than the number of black swans.

Let's denote the total number of swans as T, the number of black swans as B, and the number of white swans as W.

We can express the given information as: 1. B + W = T (Equation 1) 2. B = 0.4T (Equation 2) 3. W = B + 21 (Equation 3)

Solving for the Number of Black Swans

We can solve the system of equations to find the value of B.

Substitute Equation 2 into Equation 1: - 0.4T + W = T

Substitute Equation 3 into the above equation: - 0.4T + (B + 21) = T

Substitute Equation 2 into the above equation: - 0.4(0.4T) + (0.4T + 21) = T

Solving for T: - 0.16T + 0.4T + 21 = T - 0.56T + 21 = T - 21 = T - 0.56T - 21 = 0.44T - T = 21 / 0.44 - T ≈ 47.7273

Substitute T back into Equation 2 to find B: - B = 0.4 * 47.7273 - B ≈ 19.0909

Answer

Based on the given information, there are approximately 19 black swans and 28 white swans in the reserve.