Let's add


Step 1We still have different denominators (bottom numbers), though, so we need to get a common denominator. This will make the bottom numbers match. Multiply the denominators together first. Now, multiply each numerator by the other term's denominator. Now we multiply 7 by 10, and get 70, then we multiply 9 by 10 and get 90. Now for the second term. You multiply 3 by 9, and get 27, then multiply 9 by 10 and get 90. This gives us a new problem that looks like so:


Step 2Since our denominators match, we can add the numerators. 70 + 27 = 97 So what's the answer so far?


Step 3Can this fraction be reduced? First, we attempt to divide it by 2... No good. So next you try the next prime number, which is 3... No good. So next you try the next prime number, which is 5... No good. So next you try the next prime number, which is 7... No good. So next you try the next prime number, which is 11... No good. So next you try the next prime number, which is 13... No good. So next you try the next prime number, which is 17... No good. So next you try the next prime number, which is 19... No good. So next you try the next prime number, which is 23... No good. So next you try the next prime number, which is 29... No good. So next you try the next prime number, which is 31... No good. So next you try the next prime number, which is 37... No good. So next you try the next prime number, which is 41... No good. So next you try the next prime number, which is 43... No good. So next you try the next prime number, which is 47... No good. So next you try the next prime number, which is 53... No good. So next you try the next prime number, which is 59... No good. So next you try the next prime number, which is 61... No good. So next you try the next prime number, which is 67... No good. So next you try the next prime number, which is 71... No good. So next you try the next prime number, which is 73... No good. So next you try the next prime number, which is 79... No good. So next you try the next prime number, which is 83... No good. So next you try the next prime number, which is 89... No good. So next you try the next prime number, which is 97... No good. 97 is larger than 90. So we're done reducing. And we're done! Here's the final answer to 7/9 + 3/10
