What is the sum of 3/10+13/100

You first have to find the common denominator. So it would be 100. So times 10 times 3 for 3/10 and it would be 30/100. 13/100 already has the "100", so you can leave it. Now add them together and you get: 43/100. It cannot be simplified, so that is the final answer. 
Sources: my brain and a bit of scratch paper
Hope this helps! :-)