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c)\(\dfrac{3}{8}\times\dfrac{5}{8}+y=\dfrac{5}{4}\)
\(\dfrac{15}{64}+y=\dfrac{5}{4}\)
\(y=\dfrac{5}{4}-\dfrac{15}{64}\)
\(y=\dfrac{65}{64}\)
d, \(\dfrac{3}{8}+\dfrac{5}{8}\times y=\dfrac{5}{4}\)
\(\dfrac{5}{8}\times y=\dfrac{5}{4}-\dfrac{3}{8}\)
\(\dfrac{5}{8}\times y=\dfrac{7}{8}\)
\(y=\dfrac{7}{8}:\dfrac{5}{8}\)
\(y=\dfrac{7}{5}\)
a, 3/4 x y = 3/5 + 3/10
3/4 x y = 9/10
y = 9/10 : 3/4
y = 6/5
b, 3/5 : y = 3/4 - 2/5
3/5 : y = 7/20
y = 3/5 : 7/20
y = 12/7
\(\left(\frac{4}{5}.\frac{3}{8}+\frac{4}{5}.\frac{5}{8}-\frac{4}{5}.\frac{7}{8}\right):\frac{1}{2}\)
= \(\frac{4}{5}.\left(\frac{3}{8}+\frac{5}{8}-\frac{7}{8}\right):\frac{1}{2}\)
= \(\frac{4}{5}.\frac{1}{8}:\frac{1}{2}\)
= \(\frac{1}{5}\)
= 0,2
b: \(=8+\dfrac{7}{12}-5-\dfrac{3}{8}=3+\dfrac{5}{24}=\dfrac{77}{24}\)
\(4\dfrac{3}{8}+5\dfrac{2}{3}=\dfrac{4\times8+3}{8}+\dfrac{5\times3+2}{3}\\ =\dfrac{35}{8}+\dfrac{17}{3}=\dfrac{35\times3+17\times8}{24}=\dfrac{241}{24}\\ ----\\ 2\dfrac{3}{8}+1\dfrac{1}{4}=\dfrac{2\times8+3}{8}+\dfrac{1\times4+1}{4}=\dfrac{19}{8}+\dfrac{5}{4}\\ =\dfrac{19+5\times2}{8}=\dfrac{29}{8}\\ ----\\ 2\dfrac{3}{8}-1\dfrac{1}{4}+5\dfrac{1}{3}=\left(2-1+5\right)+\left(\dfrac{3}{8}-\dfrac{1}{4}+\dfrac{1}{3}\right)\\ =6+\dfrac{3\times3-1\times6+1\times8}{24}\\ =6+\dfrac{11}{24}=6\dfrac{11}{24}\)
\(\frac{8}{3}+\frac{8}{15}+\frac{8}{35}+\frac{8}{63}+\frac{8}{99}\)
\(=8.\left(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)
\(=8.\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\right)\)
\(=8.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)
\(=8.\left(1-\frac{1}{11}\right)\)
\(=8.\frac{10}{11}\)
\(=\frac{80}{11}\)
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5/8 : 1/4 - 3/8 : 1/4
= 5/8 x 4 - 3/8 x 4
= 4 x (5/8 - 3/8)
= 4 x 1/4
= 1