Question

Сестре 7лет, а брату 17. Когда сестра была (или будет) втрое моложе брата?

Answer 1

Чтобы решить составим систему уравнений,где х-возраст сестры,а y-брата

$\left \{ {{3x=y} \atop {y-x=10}} \right$

у из первого подставляем во второе

2х=10

х=5

у=3х=15

Ответ.Сестра будет втрое моложе брата когда ей будет 5,а ему 15

Answer 2

Calculating Age Difference:

To calculate when the sister will be three times younger than the brother, we can use the following approach:

Let's denote the current age of the sister as S and the current age of the brother as B. We want to find the future age of the sister (S') when she will be three times younger than the brother's age.

We can represent this mathematically as: S' = 3(B + x) - x where x is the number of years from the current time.

Using the Given Ages:

Given that the sister is 7 years old and the brother is 17 years old, we can calculate the future age of the sister when she will be three times younger than the brother.

S = 7, B = 17

S' = 3(17 + x) - x S' = 51 + 3x - x S' = 51 + 2x

Solving for the Future Age:

To find the future age of the sister when she will be three times younger than the brother, we need to solve for x in the equation S' = 51 + 2x.

Let's solve for x: 3S = 51 + 2x 3S - 51 = 2x x = (3S - 51) / 2

Substituting the value of S = 7: x = (3*7 - 51) / 2 x = (21 - 51) / 2 x = -30 / 2 x = -15

Interpreting the Result:

The negative value of x indicates that the future age of the sister when she will be three times younger than the brother is in the past. This means that the sister was three times younger than the brother 15 years ago.

Therefore, when the brother was 17 - 15 = 2 years old, the sister was 7 - 15 = -8 years old. This is not a valid age, as age cannot be negative.

Conclusion:

Based on the given ages, it is not possible to determine a future age for the sister when she will be three times younger than the brother, as the calculation results in a negative age for the sister.