Tính các phép tính sau

a) \[\frac{1}{4}{\rm{ + }}\frac{1}{5}\]= \[\frac{5}{{20}} + \frac{4}{{20}}\]

                = \[\frac{9}{{20}}\]

b) \[\frac{{17}}{{16}}\] – 1 = \[\frac{{17}}{{16}} - \frac{{16}}{{16}}\]

                 = \[\frac{1}{{16}}\]

c) \[\frac{4}{3} \times \frac{9}{{20}}\]= \[\frac{{4 \times 9}}{{3 \times 20}}\]

                = \[\frac{{36}}{{60}}\,\, = \,\,\frac{3}{5}\]               

d) \[\frac{{17}}{{28}}:\frac{{34}}{7}\]= \[\frac{{17}}{{28}}\]× \[\frac{7}{{34}}\]

                 = \[\frac{{17 \times 7}}{{28 \times 34}}\]= \[\frac{1}{8}\]