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bài 1.tính bằng cách hợp lí nhất :
a) 1/7 + 2/7 + 3/7 + ..... 3 5/7 + 3 6/7
b) 3/5x 3 5/9 + 6/5 x 11/9
Bài 1:
a) \(2\frac{1}{4}+1\frac{1}{2}-1\frac{4}{5}\)
=\(\frac{9}{4}\)+\(\frac{3}{2}\)-\(\frac{9}{5}\)
=\(\frac{45}{20}+\frac{30}{20}-\frac{36}{20}\)
=\(\frac{39}{20}\)
b) \(2\frac{2}{3}\times3\frac{1}{4}:2\frac{3}{4}\)
\(\frac{8}{3}\times\frac{13}{4}:\frac{11}{4}\)
=\(\frac{8}{3}\times\frac{13}{4}\times\frac{4}{11}\)
=\(\frac{104}{33}\)
Bài 2:
a) \(\frac{7}{9}+\frac{4}{5}+\frac{11}{9}+\frac{6}{5}\)
=\(\left(\frac{7}{9}+\frac{11}{9}\right)+\left(\frac{4}{5}+\frac{6}{5}\right)\)
=2+2
=4
b) \(\frac{21}{36}\times\frac{39}{14}\times\frac{54}{13}\)
=\(\frac{21\times39\times54}{36\times14\times13}\)
=\(\frac{675}{100}\)
\(3\frac{25}{125}=3\frac{1}{5}=\frac{9}{5}\) \(4\frac{20}{100}=4\frac{1}{5}=\frac{21}{5}\)
\(2\frac{5}{7}=2\frac{5}{7}=\frac{19}{7}\) \(7\frac{6}{9}=7\frac{6}{9}=\frac{70}{9}\)
Giải:
\(3\frac{25}{125}=3\frac{1}{5}\)
\(2\frac{5}{7}=2\frac{10}{14}\)
\(4\frac{20}{100}=4\frac{1}{5}\)
\(7\frac{6}{9}=7\frac{12}{18}\)
học tốt!!!
\(9\frac{1}{4}+6\frac{2}{7}+7\frac{3}{5}+8\frac{2}{3}+\frac{2}{5}+\frac{1}{3}+\frac{5}{7}+\frac{3}{4}\)
\(=\left(9\frac{1}{4}+\frac{3}{4}\right)+\left(6\frac{2}{7}+\frac{5}{7}\right)+\left(7\frac{3}{5}+\frac{2}{5}\right)+\left(8\frac{2}{3}+\frac{1}{3}\right)\)
\(=\left(\frac{37}{4}+\frac{3}{4}\right)+\left(\frac{44}{7}+\frac{5}{7}\right)+\left(\frac{38}{5}+\frac{2}{5}\right)+\left(\frac{26}{3}+\frac{1}{3}\right)\)
\(=\frac{40}{4}+\frac{49}{7}+\frac{40}{5}+\frac{40}{5}+\frac{27}{3}\)
\(=10+7+8+8+9\)
\(=42\)
**** nha Bùi Xuân Lê
\(a,1\dfrac{4}{7}.3\dfrac{4}{11}.3\dfrac{11}{15}.5\dfrac{5}{8}\)
\(=\dfrac{11}{7}.\dfrac{27}{11}.\dfrac{56}{15}.\dfrac{45}{8}\)
\(=\dfrac{11.27.56.45}{7.11.15.8}\)
\(=\dfrac{1.3.7.3}{1.1.1.1}\)
\(=63\)
\(b,\dfrac{3}{4}.1\dfrac{1}{2}+\dfrac{3}{4}.\dfrac{1}{2}\)
\(=\dfrac{3}{4}.\left(1\dfrac{1}{2}+\dfrac{1}{2}\right)\)
\(=\dfrac{3}{4}.2\)
\(=\dfrac{3}{2}\)