Directly proportional numbers are numbers that increases or decreases in the same ratio. To solve:
1) State the problem in ratios -
Let n be the missing length.
72/108 = 16/n
2) Cross multiply
72*n = 108*16
 72n = 1728
3) To get n, divide both sides of the equation by 72
72n/72 = 1728/72
     n = 24
Therefore, the chain with 16 paper clips is 24inches
To check, substitute the values -
72/108=16/n
 72*n = 108*16
72*24 = 1728
 1728 = 1728
