Step 1: Add all the terms in the ratio      

            EXAMPLE:  3 + 4 + 5 = 12

Step 2: Divide this sum by each term in the ratio

              EXAMPLE; \frac{3}{12},

                                 \frac{4}{12},

                                 \frac{5}{12}.

Step 3: Multiply the fraction with the given perimeter. To find triangle sides

           \frac{3}{12}* 30 =  7.5

           \frac{4}{12}* 30 = 10

           \frac{5}{12}* 30 = 12.5

Method 2:

Step 1:  Assume common ratio as x

                NOTE: We know that there is a common ratio for all sides of the triangle.  

                            That means that if that common ratio is denoted as x

Step 2: Write the lengths of the triangle using the variable.

            EXAMPLE: Assume a = 3x, 4x, and 5x

Step 3: Add all the lengths.

            NOTE: Perimeter = sum of all sides

                          30 = 3x + 4x + 5x

                            12x = 30

                               x = \frac{30}{12}

                              x = 2.5

Step 4: Substitute x (variable) value in the assumed lengths

              a = 3x = 3* (2.5) = 7.5

              b = 4x = 4*(2.5) = 10

              c = 5x = 4* (2.5) = 12.5