A = ( – 5/24 + 0,75 + 7/12) . ( – 2 1/8) B = 1/3.5 + 1/ 5.7 + 1 / 7.9 + …………+ 1/ 49.51

$A = (\frac{-5}{24} + 0,75 + \frac{7}{12}).(-2\frac{1}{8})$

    $= (\frac{-5}{24} + \frac{3}{4} + \frac{7}{12}).(-2\frac{1}{8})$

    $= \frac{9}{8}.(-2\frac{1}{8}) = \frac{-153}{64}$

$B = \frac{1}{3.5} + \frac{1}{5.7} + \frac{1}{7.9} +…+ \frac{1}{49.51} $

    $= \frac{1}{2}.(\frac{2}{3.5} + \frac{2}{5.7} + \frac{2}{7.9} +…+ \frac{2}{49.51})$

    $= \frac{1}{2}.(\frac{1}{3} – \frac{1}{5} + \frac{1}{5} – \frac{1}{7} + \frac{1}{7} – \frac{1}{9} +…+ \frac{1}{49} – \frac{1}{51})$

     $= \frac{1}{2}.(\frac{1}{3} – \frac{1}{51})$

     $= \frac{1}{2}.\frac{16}{51} = \frac{8}{51}$