Each fraction is as simple as it gets. Perhaps you're being taught to look at factors in one fraction that cancel those in the other.
a) [tex] \frac{5}{9} \times \frac{3}{10} = \frac{5 \times 3}{3 \times 3 \times 5 \times 2} = \frac{1}{3} \times \frac{1}{2} [/tex]
Factors of 3 and 5 have canceled.
Then the product of course is (1/3)*(1/2) = 1/6
b) no reduction is possible. The product is (3*2)/(5*7) = 6/35
c) Factors of 5 and 7 cancel. You could simplify this to 1/1 * 1/2. Then the product is 1/2.
d) A factor of 4 cancels. 1/5 * 1/2 = 1/10
