Answer: 2/3
Step-by-step explanation: Notice that 1/3 and 3/9 are unlike fractions. Our first step when adding unlike fractions is to get a common denominator.
The common denominator of 3 and 9 will be the least common multiple of 3 and 9 which is 9.
To get 9 in the denominator of 1/3, we multiply the numerator and the denominator by 3 which gives us 3/9.
Notice that 3/9 already has a 9 in the denominator so we leave it alone.
Now we are adding like fractions.
To add like fractions, we simply add the numerators and keep the same denominator.

Notice however that 6/9 is not in lowest terms so we need to divide the numerator and the denominator by the greatest common factor of 6 and 9 which is 3.
So if we divide the numerator and the denominator by 3, we end up with the equivalent fraction 2/3 which is in lowest terms.
Therefore,
