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8. A brother is older than his sister by 5 years. If you add 6 to the fifth part of the brother's age and 5 to the third part of the sister's age, the result is the same. Find their ages.

Sagot :

To solve the problem, let's carefully break it down step-by-step.

1. Define Variables:
Let [tex]\( b \)[/tex] represent the brother's age.
Let [tex]\( s \)[/tex] represent the sister's age.

2. Given Relationship:
From the problem, we know that the brother is 5 years older than the sister. Therefore, we can write this as:
[tex]\[ b = s + 5 \][/tex]

3. Set Up the Equation:
According to the problem, if you take the fifth part of the brother's age, add 6 to it; and take the third part of the sister's age, add 5 to it; the results are equal. This can be expressed as:
[tex]\[ \frac{b}{5} + 6 = \frac{s}{3} + 5 \][/tex]

4. Substitute the Relationship into the Equation:
Substitute [tex]\( b = s + 5 \)[/tex] into the equation:
[tex]\[ \frac{s + 5}{5} + 6 = \frac{s}{3} + 5 \][/tex]

5. Solve for [tex]\( s \)[/tex]:
Simplify the equation to find the sister's age:
[tex]\[ \frac{s + 5}{5} + 6 = \frac{s}{3} + 5 \][/tex]
Subtract 5 from both sides:
[tex]\[ \frac{s + 5}{5} + 1 = \frac{s}{3} \][/tex]
Multiply both sides by 15 to eliminate the denominators:
[tex]\[ 3(s + 5) + 15 = 5s \][/tex]
Simplify and solve for [tex]\( s \)[/tex]:
[tex]\[ 3s + 15 + 15 = 5s \][/tex]
[tex]\[ 3s + 30 = 5s \][/tex]
Subtract 3s from both sides:
[tex]\[ 30 = 2s \][/tex]
Divide by 2:
[tex]\[ s = 15 \][/tex]

6. Find the Brother's Age:
Now that we have the sister's age, we can find the brother's age using the given relationship:
[tex]\[ b = s + 5 = 15 + 5 = 20 \][/tex]

7. Conclusion:
Therefore, the sister's age is 15 years and the brother's age is 20 years.