$A= \dfrac{1.25 \times 10 : 0.25 \times 24.4 \times 2}{6.1 \times 2 \times 6.25 \times 4 : 0.5} + \bigg(1 - \dfrac{1}{2}\bigg)\times \bigg(1 - \dfrac{1}{3}\bigg) \times \bigg(1 - \dfrac{1}{4}\bigg) \times ... \times \bigg(1 - \dfrac{1}{19}\bigg) \times \bigg(1 - \dfrac{1}{20}\bigg)$

$A = \dfrac{(1.25 \times 5) \times 2 \times 4 \times 6.1 \times 4\times 2}{6.1 \times 2 \times 6.25 \times 4 \times 2} + \dfrac{1}{2} \times \dfrac{2}{3} \times \dfrac{3}{4} \times ... \times \dfrac{19}{20}$

$A =\dfrac{(6.25 \times 2 \times 6.1 \times 4 \times 2) \times 4}{6.25 \times 2 \times 6.1 \times 4 \times 2} + \dfrac{1 \times 2 \times 3 \times ... \times 19}{2 \times 3 \times 4 \times ... \times 20}$

$A = 4 + \dfrac{1}{20}$

$A = 4 +0.05$

$A = 4.05$

Đáp án:

$⇒A=4,05$

Giải thích các bước giải:

$A=\dfrac{1,25×10÷0,25×24,4×2}{6,1×2×0,25×4÷0,5}+(1-\dfrac{1}{2})×(1-\dfrac{1}{3})×...×(1-\dfrac{1}{20})$

$⇒A=\dfrac{1,25×5×2×4×6,1×4×2}{6,1×2×6,25×4×2}+\dfrac{1}{2}×\dfrac{2}{3}×...×\dfrac{19}{20}$

$⇒A=\dfrac{(6,25×2×4×6,1×2)×4}{(6,1×2×6,25×4×2)}+\dfrac{1×2×...×19}{2×3×..×20}$

$⇒A=4+\dfrac{1}{20}$

$⇒A=4+0,05$

$⇒A=4,05$