4/5 of Sarah's pens are equal to 1/3 of Matt's pens. Express the number of Matt's pens as a fraction of the total number of pens of he and Sarah have

Let us say that the number of pens that Matt has is x. Therefore the number of pen that Sarah has is:

Sarah pens = (5/4) (1/3) x = (5/12) x

So the total number of pens they have is:

total = x + (5/12) x = (17/12) x

Hence the fraction of Matts pen is:

fraction = x / [ (17/12) x]

fraction = 12/17