Shabbir has a brother one-fourth of his age and a sister two times of his age. If the combined age of all the three siblings is twenty more than thrice the age of the youngest, how old is Shabbir's sister?

Explanation: মনেকরি, Sabbir-এর বয়স \(= x\) বছর। Sabbir-এর ভাইয়ের বয়স \(= \frac{x}{4}\) বছর। Sabbir-এর বোনের বয়স \(= 2x\) বছর। The youngest is the brother, age \(\frac{x}{4}\). Combined age \(= x + \frac{x}{4} + 2x = 3x + \frac{x}{4} = \frac{13x}{4}\). Condition: Combined age \(= 3 \times (\text{youngest age}) + 20\). \(\frac{13x}{4} = 3 \times \frac{x}{4} + 20 \Rightarrow \frac{13x}{4} - \frac{3x}{4} = 20 \Rightarrow \frac{10x}{4} = 20 \Rightarrow 10x = 80 \Rightarrow x = 8\). Shabbir's sister's age \(= 2x = 2 \times 8 = 16\).