The following  image was made from Add with Lines Designer:

Add Unlike Image showing number lnes

You will notice that the addends 3/8 and 1/3 have unlike denominators. You must first rename 3/8 and 1/3 with a like or common denominator(LCD).  The program COMPARE FRACTIONS shows how to find the LCD. In this case, each addend is written with a common denominator 24.

Once each addend is written with like denominators, the numerators may be added for the sum numerator.

The program ADD FRACTIONS - EASY shows how to add fractions with like denominators.

Written out, the example would look like this:

Add Unlike Work

See an animation of number-line addition. The animation was made with the Fraction Designer series.