a)
\(\begin{array}{l}\dfrac{{21}}{{11}} \times \dfrac{{22}}{{17}} \times \dfrac{{68}}{{63}} = \dfrac{{21 \times 22 \times 68}}{{11 \times 17 \times 63}}\\= \dfrac{{21 \times 11 \times 2 \times 17 \times 4}}{{11 \times 17 \times 21 \times 3}}\\ = \dfrac{{2 \times 4}}{3} = \dfrac{8}{3}\end{array}\)
b)
\(\begin{array}{l}\dfrac{5}{{14}} \times \dfrac{7}{{13}} \times \dfrac{{26}}{{25}} = \dfrac{{5 \times 7 \times 26}}{{14 \times 13 \times 25}}\\ = \dfrac{{5 \times 7 \times 13 \times 2}}{{7 \times 2 \times 13 \times 5 \times 5}} = \dfrac{1}{5}\end{array}\)
