Question

tính bằng 2 cách : (2/3 x 4/5 ) x 5/6

                              ( 1/2 + 1/3 ) x1/5

 

Answer 1

a. C1: \(\dfrac{8}{15}.\dfrac{5}{6}=\dfrac{4}{9}\)

C2: \(\dfrac{2}{3}.\dfrac{4}{5}.\dfrac{5}{6}=\dfrac{2.4.5}{3.5.3.2}\)

Triệt tiêu phần giống nhau ở tử và mẫu ta có 

\(=\dfrac{4}{9}\)

b. \(C1:\left(\dfrac{1}{2}+\dfrac{1}{3}\right).\dfrac{1}{5}=\dfrac{5}{6}.\dfrac{1}{5}=\dfrac{1}{6}\)

C2: \(\dfrac{1}{2}.\dfrac{1}{5}+\dfrac{1}{3}.\dfrac{1}{5}=\dfrac{1}{10}+\dfrac{1}{15}=\dfrac{1}{6}\)

 

Answer 2

Cách 1:

$(\frac{2}{3}\times \frac{4}{5})\times \frac{5}{6}=\frac{8}{15}\times \frac{5}{6}=\frac{8\times 5}{15\times 6}=\frac{2\times 2\times 2\times 5}{3\times 5\times 2\times 3}=\frac{4}{9}$

Cách 2:

$(\frac{2}{3}\times \frac{4}{5})\times \frac{5}{6}=\frac{2}{3}\times (\frac{4}{5}\times \frac{5}{6})=\frac{2}{3}\times \frac{4}{6}=\frac{2\times 4}{3\times 6}=\frac{2\times 4}{3\times 2\times 3}=\frac{4}{9}$

 

Cách 1:

$(\frac{1}{2}+\frac{1}{3})\times \frac{1}{5}=\left(\frac{3+2}{6}\right)\times \frac{1}{5}=\frac{5}{6}\times \frac{1}{5}=\frac{1}{6}$

Cách 2:

$(\frac{1}{2}+\frac{1}{3})\times \frac{1}{5}=\frac{1}{2}\times \frac{1}{5}+\frac{1}{3}\times \frac{1}{5}=\frac{1}{10}+\frac{1}{15}=\frac{3}{30}+\frac{2}{30}=\frac{5}{30}=\frac{1}{6}$