15. a) x - 1/2 = 1/4 15. б) 1 1/2 - x = 3/4 15. в) x - 1/4 = 1 1/4 15. г) 7/10 - x = 1/2

Решение:

• a) \( x = \frac{1}{4} + \frac{1}{2} = \frac{1}{4} + \frac{2}{4} = \frac{3}{4} \)
• б) \( x = 1\frac{1}{2} - \frac{3}{4} = \frac{3}{2} - \frac{3}{4} = \frac{6}{4} - \frac{3}{4} = \frac{3}{4} \)
• в) \( x = 1\frac{1}{4} + \frac{1}{4} = \frac{5}{4} + \frac{1}{4} = \frac{6}{4} = 1\frac{2}{4} = 1\frac{1}{2} \)
• г) \( x = \frac{7}{10} - \frac{1}{2} = \frac{7}{10} - \frac{5}{10} = \frac{2}{10} = \frac{1}{5} \)

Ответ: а) 3/4, б) 3/4, в) 1 1/2, г) 1/5