Question

Determine weather 12,15,4,5 are in proportion or not

Answer 1

yes they are in the proportion because 12/15=4/5=4/5

Answer 2

Yes, because in this proportion, 12 : 15 :: 4 : 5 , Product of means is equal to the product of extremes,
        ⇒ 12 x 5 = 15 x 4
        ⇒ 60 = 60
     Hence verified

Hope it helps..... :)