In a proportion there are letters assigned to represent various numbers. a, b, c, and d.
a, b, c, and d are 4 non-zero rational numbers that are terms of proportion.
a/b = c/d or a:b = c:d
a and d are the end terms or known as the extremes.b and c are the middle terms or known as the means.
With this information, we can gather that the extremes of the following proportion are 3 and 60.
3/15 = 12/60 ; a/b = c/da = 3 ; b = 15 ; c = 12 ; d = 60
3 and 60 are the extremes15 and 12 are the means