Complete the recursive formula of the arithmetic sequence 20,26,32,38

A recursive formula for a sequence expresses the -th term as a function of the previous one(s).

In this case, you can see that every term is 6 more than the previous one.

So, the recursive formula is "the -th term is 6 more than the -th term".

In formula, it's written

Since the recursion could go back indefinitely, we usually set a starting point, so that the sequence is fully determined:

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.