Tính : S = (1-1/28) x (1-1/36) x (1-1/45) x ..... x (1-1/4950)

* Hướng dẫn giải

$\frac{27}{28} = \frac{3x9 }{4x7} = \frac{3}{4} x \frac{9}{7}$

$\frac{27}{28} x \frac{35}{36}= \frac{\left(3x9\right) }{ \left(4x7\right)} x \frac{\left(5x7\right) }{ \left(4x9\right)} = \frac{3}{4} x \frac{5}{4}$

$\frac{27}{28} x \frac{35}{36} x \frac{44}{45} =\frac{ 3x5}{4x4} x \frac{4x11}{5x9 }= \frac{3}{4} x \frac{11}{9}$

$...... xxxxxx .... x \frac{\left(49x101\right)}{\left(50x99\right)} = \frac{3}{4} x \frac{101}{99}$