The best way to do this is to convert the mixed numbers into improper fractions. Improper fractions are when the numerator is greater than the denominator. An example of an improper fraction would be 5/4. Since 4/4 is one whole that means 5/4 as a mixed number would be 1 1/4. I'll use the expression 3 1/4 + 5 2/9 as an example.
3 1/4 is 3 wholes and 1/4 left over. We know that 4/4 is 1 whole so to find 3 holes we multiply the 1 by 3. 4 x 3 =12 so there are 12/4 in 3 holes. We then add the leftover 1/4 to get 13/4 as our first number.
For the second number, we have 5 2/9. This one is a bit harder. We know that 9/9 is in one whole, but how do we find how many are in 5 wholes? We can use multiplication. 1x 5=5. 5 x 9 =45. That means we have 45/9 in 5 holes. Add the leftover 2/9 to have 47/9 as our 2nd number.
Now that we have these two improper fractions, what do we do with them? The two numbers we are working with are 13/4 and 47/9. We need to find the common denominator. The common denominator is when both fractions have the same bottom number. If two fractions have different denominators we cannot add them.
To make the denominators the same, let's find a common multiple. A common multiple is a number that is a product of all chosen numbers. This is kind of confusing but another way to think of a common multiple is a number that is divisible by all chosen numbers. Take the two denominators and multiply them. 9x4=36. 36 is a common multiple of both 9 and 4 because both of them can go into 36 without being a decimal or a fraction.
To convert the fractions we multiply again. Whatever you do to one side you must always do to the other. In 13/4 we multiplied 4x9 to get 36. So now we multiply the numerator 13x9 to get 117. That means we have 117/36. We multiplied 9x4 to also get 36. So our numerator for our second number is 47x4=188 or 188/36.
Now we have 117/36 and 188/36. We add them together like normal and get 305/36. In some cases you'd need to simplify it, but for the example equation I used this is already the fraction's lowest form. I hope this helped! Comment if you need another example or have any questions! :)
