Tính nhanh: (1 - 1/4) x (1 - 1/5) x (1 - 1/6) x (1 - 1/7) x (1 - 1/8

Đề bài: Tính nhanh: $\left(1-\frac{1}{4}\right)\times \left(1-\frac{1}{5}\right)\times \left(1-\frac{1}{6}\right)\times \left(1-\frac{1}{7}\right)\times \left(1-\frac{1}{8}\right)$.

Trả lời

Hướng dẫn giải:

$\left(1-\frac{1}{4}\right)\times \left(1-\frac{1}{5}\right)\times \left(1-\frac{1}{6}\right)\times \left(1-\frac{1}{7}\right)\times \left(1-\frac{1}{8}\right)$

$=\frac{3}{4}\times \frac{4}{5}\times \frac{5}{6}\times \frac{6}{7}\times \frac{7}{8}$

=3/8.