15) (5/26 - 3/25) * 13/2

15) \((\frac{5}{26} - \frac{3}{25}) \cdot \frac{13}{2} = (\frac{125}{650} - \frac{78}{650}) \cdot \frac{13}{2} = \frac{47}{650} \cdot \frac{13}{2} = \frac{47 \cdot 13}{650 \cdot 2} = \frac{47 \cdot 1}{50 \cdot 2} = \frac{47}{100}\)
Ответ: 47/100