Which least number must be subtracted from each of the term 15, 37, 21, 55 to make them proportional ?

4

To make these numbers in proportion, the condition should be:

(15 - a) : (37 - a) :: (21 - a) : (55 - a)

Check from the option, which is the best way to find the number.

So, Option (a):- 4 will justify the equation.

(15 - 4) : (37 - 4) :: (21 - 4) : (55 - 4)

    11    :      33    ::     17    :     51

     1     :       3    ::       1    :      3

Therefore, 4 is correct answer.