[amp_mcq option1=”12 years” option2=”15 years” option3=”18 years” option4=”20 years” correct=”option2″]
The correct answer is (b), 15 years.
Let $f$ be the father’s current age and $s$ be the son’s current age. We are given that $f = 3s$ and $f – 5 = 4(s – 5)$. Substituting the first equation into the second equation, we get $3s – 5 = 4s – 20$. Solving for $s$, we get $s = 15$.
Option (a), 12 years, is incorrect because $12 \times 3 = 36$, which is not the father’s current age. Option (c), 18 years, is incorrect because $18 \times 3 = 54$, which is not the father’s current age. Option (d), 20 years, is incorrect because $20 \times 3 = 60$, which is not the father’s current age.