a) $\frac{9}{14}-\frac{2}{7}+\frac{1}{7}$=

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b) $\frac{7}{10}+\frac{12}{25}:\frac{4}{5}$=

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c) $1:\frac{3}{5}\times \frac{9}{10}$=

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d) $\left(\frac{15}{10}-\frac{1}{2}\right)\times \frac{32}{35}$=

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a) $\frac{9}{14}-\frac{2}{7}+\frac{1}{7}=\frac{9}{14}-\frac{4}{14}+\frac{2}{14}$ = $\frac{9-4+2}{14}$ = $\frac{7}{14}=\frac{1}{2}$

b) $\frac{7}{10}+\frac{12}{25}:\frac{4}{5}=\frac{7}{10}+\frac{12}{25}\times \frac{5}{4}=\frac{7}{10}+\frac{3}{5}=\frac{7}{10}+\frac{6}{10}=\frac{13}{10}$

c) $1:\frac{3}{5}\times \frac{9}{10}$=$1\times \frac{5}{3}\times \frac{9}{10}=\frac{5}{3}\times \frac{9}{10}=\frac{45}{30}=\frac{3}{2}$

d) $\left(\frac{15}{10}-\frac{1}{2}\right)\times \frac{32}{35}=\left(\frac{3}{2}-\frac{1}{2}\right)\times \frac{32}{35}=1\times \frac{32}{35}=\frac{32}{35}$