Bài 3. Tính bằng hai cách: a) (5,28+4,72)×4,5 b) (7,8−2,3)×6,4

a,
Cách 1
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
( 5,28+4,72) \times 4,5\\
=10\times 4,5\\
=45
\end{array}$
Cách 2
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
( 5,28+4,72) \times 4,5\\
=5,28\times 4,5+4,72\times 4,5\\
=23,76+21,24\\
=45
\end{array}$
b,
Cách 1
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
( 7,8−2,3) \times 6,4\\
=5,5\times 6,4\\
=35,2
\end{array}$
Cách 2
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
( 7,8−2,3) \times 6,4\\
=7,8\times 6,4−2,3\times 6,4\\
=49,92-14,72\\
=35,2
\end{array}$