The calculation formula of daily increment is sn = a [(1+q) (n-1)]/q.

Where: Sn represents the total number after n times of growth, A represents the quantity at the beginning of the first time, Q represents the growth rate, and N represents the number of times of growth.

Analysis: according to the meaning of the question, this is a summation formula of the first n terms of geometric series with A as the first term and Q as the common ratio. The formula is sn = a [(1+q) (n-1)]/q.

When the amount of the first day is X, 30 = X [(1+1.2) 29]/1.2, from which the amount of the first day can be calculated.

Higher order arithmetic series

The definition of geometric series of R-order difference, by applying the method of step-by-step difference to a certain series, makes a geometric series after several steps of difference. This series is also called higher-order differential geometric series. It is defined that if the first r-order difference of a sequence is not a geometric series, and the r+ 1 order difference is a geometric series, then the sequence is called an r-order difference geometric series.