Check whether the numbers are in continued proportions: 1,2,3

Check whether the numbers are in continued proportions: 9,12,16

Check whether the numbers are in continued proportions: 3,5,8

Check whether the numbers are in continued proportions: 2,4,8.

Check whether the numbers 4, 10 and 15 are in continued proportion or not ?

Which number should be subtracted from 7,12 and 18 such that the resultant numbers are in continued proportion?

Which number should be subtracted from 12,16 and 21 so that resultant numbers are in continued proportion?

Which number should be subtracted from 13,25 and 55 so that resultant numbers are in continued proportion?