We have the following general rule for the substraction of fractions:
[tex]\begin{gathered} \frac{a}{b}-\frac{c}{d}=\frac{a\cdot d-b\cdot c}{b\cdot d} \\ b,d\ne0 \end{gathered}[/tex]in this case, we have the following:
[tex]\frac{7}{10}-\frac{2}{5}=\frac{7\cdot5-2\cdot10}{10\cdot5}=\frac{35-20}{50}=\frac{15}{50}[/tex]notice that 15 and 50 are multiples of 5,therefore:
[tex]\frac{15}{50}=\frac{3}{10}[/tex]finally, we have that the result of the substraction is 3/10
