B) 1-(1/2) × 1-(1/3) × 1-(1/4) × 1-(1/5) Cảm ơn mọi ngừi giúp mik nha

$B = (1-\dfrac{1}{2})×(1-\dfrac{1}{3})×(1-\dfrac{1}{4})×(1-\dfrac{1}{5})$

$ = \dfrac{1}{2}×\dfrac{2}{3}×\dfrac{3}{4}×\dfrac{4}{5}$

$ = \dfrac{1×2×3×4}{2×3×4×5}$

$ = \dfrac{1}{5}$

Vậy $B = \dfrac{1}{5}$