It is important to have a sence about the size of fractions to be able to estimate what the answer is.
For example we can say that 3/5 + 1/2 is approximately equal to 1 or just over one. We can say this because 3/5 is just over a half. Therefore if we add what they are close to we can see that it will be just over 1.
Not only can we make an estimation of what the answer might be but we can use the rectangle method of multiplication for fractions!
Not only can we use this method with whole number but we can use this for fractions. The picture below shows a few examples of using this method with fractions.
When using the Rectangle Method of Multiplication for fractions you have to be able to think in parts of a whole. For example when we do 1/2 x 2/3 (the bottom problem in the picture above) we start with a 1×1 square, then we have to split the square into halves in one direction, and then into thirds in the other direction. After we do this we can shade in 2/3. By splitting the 1×1 square into half in one direction and thirds in the other we get a box that is sixths, this gives us a final answer of 2/6 because there are six parts and two of them are shaded.
We can also use this method for division of fractions if you change the division into multiplication. Here are some videos that can help explain adding and subtraction of fractions. It will also help explain multiplication and division.