Câu 4: Tính bằng cách thuận tiện nhất:
\(3,8\times4,54+3,6:1,5+5,46\times3,8-2,1:1,5\)
\(=3,8\times\left(5,54+5,46\right)+\left(3,6-2,1\right):1,5\)
\(=3,8\times10+1,5:1,5\)
\(=\left(3,8\times10\right)+\left(1,5:1,5\right)\)
\(=38+1=39\)
Câu 5: Tính nhanh:
\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times\left(1-\dfrac{1}{5}\right)\)
\(=\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times\dfrac{4}{5}\)
\(=\dfrac{1\times2\times3\times4}{2\times3\times4\times5}\)
\(=\dfrac{1}{5}\)