Simple fractions require basic math. Since you are multiplying fractions, follow the basic steps in order to get the answer (simplified or not).
Step 1:
Simplify the fractions if not in lowest terms.
For example in the given equation, since it is in its lowest term, we opt to leave it as it is.
Step 2:
Multiply the numerators of the fraction in the given equation to get a niew numerator
9 x 2 = 18
Step 3:
This is the same as step 2. Multiply the denominators in the given equation to get a new denominator
10 x 5= 50
Step 4:
Simplify the resulting fraction if possible
9/10 x 2/5 = 18 / 50
The answer 18/50 can be simplified and the resulting fraction will be 9/25