Sum is just another word for addition, so we have to add the two fractions.
3/10 + 17/100
Find the LCD of the denominators, hence the name 'least common denominator'. To do that, list out the multiples of each denominator and find the least common one.
Multiples of 10: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
Multiples of 100: 100
The least common denominator is 100.
Now, divide the denominator of 3/10 to get the new denominator of 100. Whatever you do to the bottom, you have to do to the top.
(3 × 10) / (10 × 10) + 17/100
30/100 + 17/100
Since the denominators are the same now, we can add both of the numerators together.
(30 + 17) / 100
47/100
The answer is: 47/100 or 0.47.