Answer: 10
Explanation:
To find a common denominator, simply multiply the denominator and numerator of one fraction by the denominator and numerator of the other. Then repeat.
3*2/5*2 = 6/10
1*5/2*5=5/10
As you can see, the denominator of both fractions is 10.
Hope it helps and lmk if you need further explanation :)