There are n terms in an arithmetic progression. The n terms of the arithmetic progression are now distributed into eight sub-series - S1, S2and S8 - as follows. The 1st, 9th, 17th terms and so on go into S1; the 2nd, 10th, 18th terms and so on go into S2; the 3st, 11th, 19th terms and so on go into S3, and so on for S4 till S8. If for exactly three of the eight sub-series, the average of the sub-series is a term of the same sub-series, which of the following could be a possible value of n?

21 goats eat as much as 15 cows. How many goats each as much as 35 cows?

The average of 20 numbers is zero. Of them, How many of them may be greater than zero , at the most?