Bài 6
Chu vi tấm bìa là \(4.\dfrac{31}{7}=\dfrac{124}{7}dm\)
DT tấm bìa là \(\dfrac{31}{7}.\dfrac{31}{7}=\dfrac{961}{49}dm\)
Bài 7
a) \(\dfrac{3}{4}-\dfrac{5}{6}.\left(\dfrac{1}{6}+\dfrac{1}{8}\right):\dfrac{7}{12}\)
\(=\dfrac{3}{4}-\dfrac{5}{6}.\dfrac{7}{24}:\dfrac{7}{12}\)
\(=\dfrac{3}{4}-\dfrac{5}{12}=\dfrac{9}{12}-\dfrac{5}{12}=\dfrac{4}{12}=\dfrac{1}{3}\)
b) \(\dfrac{15}{8}:\dfrac{45}{6}-\dfrac{1}{13}.\left(\dfrac{4}{9}-\dfrac{1}{12}\right)\)
\(=\dfrac{15}{8}:\dfrac{45}{6}-\dfrac{1}{13}.\dfrac{13}{36}\)
\(=\dfrac{1}{4}-\dfrac{1}{36}=\dfrac{9}{36}-\dfrac{1}{36}=\dfrac{8}{36}=\dfrac{2}{9}\)
